Biaxially stretched laminated polyester film, infrared light shielding structure for laminated glass composed of the same, and laminated glass composed of the same

ABSTRACT

Provided are a biaxially stretched laminated polyester film and a laminated glass composed of the same. Specifically, the invention is achieved by a biaxially stretched laminated polyester film including 51 layers or more in total, in which a first layer and a second layer are alternately laminated, wherein a polyester (A) constituting the first layer is polyethylene-2,6-naphthalenedicarboxylate; a polyester (B) constituting the second layer is a polyester containing at least one of an ethylene terephthalate component and an ethylene naphthalene dicarboxylate component; an average reflectance within a wavelength range of 400 to 750 nm is not more than 25%; an average reflectance within a wavelength range of 800 to 1,200 nm is 50% or more; and a Young&#39;s modulus of the film at 90° C. is 2,400 MPa or more in at least one direction of the longitudinal direction and the lateral direction of the film.

TECHNICAL FIELD

The present invention relates to a biaxially stretched laminatedpolyester film having excellent near-infrared light shielding propertiesand processability into a laminated glass, an infrared light shieldingstructure for laminated glass composed of the same, and a laminatedglass composed of the same.

BACKGROUND ART

As glasses which are used for windows of vehicles such as automobiles,electric trains, etc. and buildings, a laminated glass having a functionto shield heat rays is investigated, and a part thereof has already beenput into practical use. In recent years, such a laminated glass getsattention from the viewpoint of energy conservation because it preventsincidence of heat rays.

This laminated glass transmits a visible light of whole rays andselectively reflects or absorbs heat rays. For example, when this isused for a windowpane, in a season in which the sunlight is strong, itcan suppress a temperature increase in the interior of a room to becaused due to incidence of heat rays, whereas in a season in which thesunlight is weak, and the heating is used, it can suppress an escape ofheat from the interior of a room to the outdoors. For that reason, theuse of this laminated glass can greatly enhance the utilizationefficiency of energy and is useful for energy conservation.

This laminated glass can be obtained by laminating a heat ray shieldingfilm on a glass.

Patent Literature 1 discloses an optical interference film whichreflects an infrared light while transmitting a visible light,comprising multiple alternating layers of at least three kinds of layerseach having an optical thickness ranging from 0.09 to 0.45 μm, wherein arefractive index of a polymer of the second layer is intermediatebetween a refractive index of a polymer of the first layer and arefractive index of a polymer of the third layer. Patent Literature 1discloses that one of the three layers may be made ofpolyethylene-2,6-naphthalenedicarboxylate. However, Patent Literature 1does not investigate a laminated polyester film having a layer structurein which two kinds of layers are alternately laminated, the laminatedpolyester film being excellent in not only near-infrared light shieldingproperties but processability into a laminated glass.

Patent Literature 2 describes a birefringent dielectric multilayer filmwhich reflects at least 50% of light in a band having a width of atleast 100 nm in a wavelength region of interest. Patent Literature 2describes that the multilayer film includes alternating layers of afirst polymer and a second polymer and may be laminated on a non-planarglass layer and used in vehicular windshields. Meanwhile, in thepolymers of the respective layers specifically investigated in PatentLiterature 2, the first polymer was a polyester, whereas the secondpolymer was PMMA.

Patent Literature 3 discloses a transparent multilayer device whichreflects an infrared light while transmitting a visible light,comprising a polymer film including a plurality of layers and atransparent conductor having at least one layer containing a metal or ametal compound. In Patent Literature 3, as for the case of mirrors,namely, combinations of the multilayer films obtained by stretching intwo directions within the film plane, there are exemplified PEN/Ecdel (atrade name for thermoplastic elastomer), PEN/sPS, PEN/copolymerized PET,and the like. Patent Literature 3 describes that the transparentmultilayer device may be used in windshields for automobiles or thelike, or windowpanes. However, Patent Literature 3 does not investigatean increase of the processability into a laminated glass.

In addition, Patent Literature 4 discloses a near heat ray shieldingfilm in which a first layer having a melting point ranging from 250 to260° C. and comprising ethylene terephthalate as a main recurring unitand a second layer having a melting point ranging from 200 to 245° C.and comprising ethylene terephthalate as a main recurring unit arealternately laminated and describes that an interlayer separationphenomenon is inhibited by increasing adhesion between layers by usingresins having a composition close to each other in the first layer andthe second layer. However, in the resins having a composition close toeach other, since a difference in refractive index between the layers issmall, the layer number is required to be increased, and it is necessaryto take a complicated layer structure in which a first laminated portionand a second laminated portion having a different layer thickness ratiofrom the first layer and the second layer, respectively are furtherlaminated. In addition, Patent Literature 4 does not investigate anincrease of the processability into a laminated glass.

Patent Literature 5 discloses a biaxially stretched polyester filmsuitable as an intermediate film for a laminated glass with a goodappearance, comprising an alternate laminate of two kinds of resins andhaving excellent glass scattering prevention and crime preventionperformance. In Patent Literature 5, for the purpose of increasing thecrime prevention performance, the Young's modulus of the film at roomtemperature is specified. However, Patent Literature 5 is concerned witha polyester film having an excellent crime prevention performance, butit does not make investigations while paying attention to an increase ofnear-infrared light shielding properties and processability into alaminated glass.

In the light of the above, in the case of an alternate laminate made ofpolymers of different kinds which has been conventionally investigated,for example, PMMA has a high hardness, and therefore, when processedinto a laminated glass, a phenomenon of generation of fineirregularities is not caused. Thus, such was not acknowledged as aproblem. However, it has been newly clarified that in the process ofproceeding with investigation of films for laminated glass using analternate laminate made of polyesters each other for the purposes ofrecycle properties, solving of separation between layers, and so on,when a polyester-based alternate laminate having excellent near-infraredlight shielding properties is processed into a laminated glass, fineirregularities are generated on the film surface. Furthermore, it is thepresent state that a film having increased processability into alaminated glass is demanded.

-   Patent Literature 1: JP-A-4-313704-   Patent Literature 2: JP-A-2011-225445-   Patent Literature 3: JP-T-11-508380-   Patent Literature 4: WO 2005/040868A-   Patent Literature 5: JP-A-2005-186613

DISCLOSURE OF INVENTION Technical Problem

A problem of the present invention is to provide a biaxially stretchedlaminated polyester film having not only a high near-infrared shieldingperformance but excellent processability at the time of processing intoa laminated glass, an infrared light shielding structure for laminatedglass composed of the same, and a laminated glass composed of the same.

Solution to Problem

In order to solve the above-described problem, the present inventorsmade extensive and intensive investigations. As a result, it has beenfound that when the conventional biaxially stretched laminated polyesterfilm having excellent near-infrared light shielding properties reaches ahigh temperature as 90° C. at which it is processed into a laminatedglass, the Young's modulus of the film greatly changes, and at the timeof processing into a laminated glass to be carried out by heating underpressure, a surface shape of an opposite material to be laminated iseasily transferred, so that the processability into a laminated glasswas lowered, leading to the present invention.

Thus, according to the present invention, an object of the presentinvention is achieved by a biaxially stretched laminated polyester film(Item 1) comprising 51 layers or more in total, in which a first layerand a second layer are alternately laminated, wherein a polyester (A)constituting the first layer ispolyethylene-2,6-naphthalenedicarboxylate; a polyester (B) constitutingthe second layer is a polyester containing at least one of an ethyleneterephthalate component and an ethylene naphthalene dicarboxylatecomponent; an average reflectance within a wavelength range of 400 to750 nm is not more than 25%; an average reflectance within a wavelengthrange of 800 to 1,200 nm is 50% or more; and a Young's modulus of thefilm at 90° C. is 2,400 MPa or more in at least one direction of thelongitudinal direction and the lateral direction of the film.

In addition, the biaxially stretched laminated polyester film of thepresent invention includes the following constitutions as preferredembodiments.

Item 2: The biaxially stretched laminated polyester film as set forth inItem 1, having a protective layer composed of a polymer having a glasstransition temperature of 90° C. or higher and having a thickness of 5μM or more and not more than 20 μm on the both sides of a laminatedstructure portion (I) in which the first layer and the second layer arealternately laminated.Item 3: The biaxially stretched laminated polyester film as set forth inItem 2, wherein the polyester (B) constituting the second layer is apolyester containing 50% by mole or more and not more than 95% by moleof an ethylene terephthalate component on the basis of the wholerecurring units.Item 4: The biaxially stretched laminated polyester film as set forth inItem 2 or 3, wherein the polyester (B) constituting the second layer iscopolymerized polyethylene terephthalate having a glass transitiontemperature of lower than 90° C.Item 5: The biaxially stretched laminated polyester film as set forth inItem 1, wherein the biaxially stretched laminated polyester film iscomposed of only a laminated structure portion (I) in which the firstlayer and the second layer are alternately laminated; or is a film inwhich a protective layer having a thickness of less than 5 μm isprovided on the both sides thereof, the polyester (B) constituting thesecond layer is composed of a polyester having a glass transitiontemperature of lower than 90° C., and a Young's modulus of the film at20° C. is 5,000 MPa or more in at least one direction of thelongitudinal direction and the lateral direction of the film.Item 6: The biaxially stretched laminated polyester film as set forth inItem 1 or 2, wherein the polyester (B) constituting the second layer isa polyester having a glass transition temperature of 90° C. or higher.Item 7: The biaxially stretched laminated polyester film as set forth inItem 6, wherein the polyester (B) constituting the second layer is apolyester containing 30% by mole or more and not more than 90% by moleof an ethylene naphthalene dicarboxylate component on the basis of thewhole recurring units.Item 8: The biaxially stretched laminated polyester film as set forth inany one of Items 1 to 7, wherein the polyester (A) constituting thefirst layer is polyethylene-2,6-naphthalenedicarboxylate having acopolymerization amount of not more than 8% by mole on the basis of thewhole recurring units.Item 9: The biaxially stretched laminated polyester film as set forth inany one of Items 1 to 8, having at least one layer containing anultraviolet light absorber.Item 10: The biaxially stretched laminated polyester film as set forthin Item 9, wherein the ultraviolet light absorber has an extinctioncoefficient ∈ at a wavelength of 380 nm of 2 or more.Item 11: The biaxially stretched laminated polyester film as set forthin Item 9 or 10, wherein an average light transmittance within awavelength range of 300 nm or more and less than 400 nm is not more than10%.Item 12: The biaxially stretched laminated polyester film as set forthin any one of Items 1 to 11, which is used for shielding of heat rays.Item 13: The biaxially stretched laminated polyester film as set forthin any one of Items 1 to 12, which is used for laminated glass.Item 14: The biaxially stretched laminated polyester film as set forthin any one of Items 1 to 13, wherein a coating layer having a refractiveindex of 1.60 to 1.63 and a thickness of 0.05 to 0.2 μm is provided onat least one surface of the biaxially stretched laminated polyester filmhaving the laminated structure portion (I).

In addition, the present invention also includes an infrared lightshielding structure for laminated glass comprising the biaxiallystretched laminated polyester film of the present invention having alaminate of a metal and/or a metal oxide laminated on one surfacethereof, wherein in the biaxially stretched laminated polyester film, athickness of the protective layer on the side coming into contact withthe laminate of a metal and/or a metal oxide is 5 μm or more and notmore than 20 μm; the laminate of a metal and/or a metal oxide has alaminated structure (II) in which a low-refractive index layer and ahigh-refractive index layer are alternately laminated; and the infraredlight shielding structure for laminated glass has an average reflectancein a wavelength range of 400 to 750 nm of not more than 30%, an averagereflectance in a wavelength range of 800 to 1,200 nm of 50% or more, andan average reflectance in a wavelength range of 1,200 to 2,100 nm of 50%or more.

Furthermore, the present invention also includes a laminated glasscomprising two glass sheets having the biaxially stretched laminatedpolyester film of the present invention sandwiched therebetween via aresin layer composed of at least one member selected from anethylene-vinyl acetate copolymer, polyvinyl butyral, and an ionomerresin.

Furthermore, a laminated glass comprising two glass sheets having theinfrared light shielding structure for laminated glass of the presentinvention sandwiched therebetween via a resin layer composed of at leastone member selected from an ethylene-vinyl acetate copolymer, polyvinylbutyral, and an ionomer resin is also included as one embodiment of thepresent invention.

Advantageous Effects of Invention

According to the present invention, a biaxially stretched laminatedpolyester film having both a high near-infrared shielding performanceand excellent processability into a laminated glass is provided, and byusing the biaxially stretched laminated polyester film of the presentinvention, when processed into a laminated glass, a laminated glasshaving an excellent appearance such that fine irregularities are notgenerated and having an excellent near-infrared shielding performancecan be provided.

BEST MODE FOR CARRYING OUT THE INVENTION First Layer

In the present invention, the polyester (A) constituting the first layeris polyethylene-2,6-naphthalenedicarboxylate.

A proportion of the ethylene-2,6-naphthalenedicarboxylate component inthe polyester (A) is preferably 95% by mole or more and not more than100% by mole, more preferably 96% by mole or more, and still morepreferably 97% by mole or more on the basis of the whole recurring unitsconstituting the polyester (A). When the proportion of theethylene-2,6-naphthalenedicarboxylate component that is a main componentis less than the lower limit, the melting point of the polyester (A)constituting the first layer is lowered, and a difference in meltingpoint from the polyester (B) constituting the second layer as describedlayer is hardly obtained. As a result, there is a concern that asufficient difference in refractive index is hardly imparted to thebiaxially stretched laminated polyester film.

As other copolymerization components than the main componentconstituting the polyester (A), there are preferably exemplified acidcomponents such as aromatic carboxylic acids, for example, isophthalicacid, terephthalic acid, orthophthalic acid, a naphthalenedicarboxylicacid other than 2,6-naphthalenedicarboxylic acid, biphenyldicarboxylicacid, etc.; aliphatic dicarboxylic acids, for example, succinic acid,adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, etc.;alicyclic dicarboxylic acids, for example, cyclohexanedicarboxylic acid,etc., and the like, as well as glycol components such as aliphaticdiols, for example, diethylene glycol, propylene glycol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, etc.; alicyclicdiols, for example, 1,4-cyclohexanedimethanol; polyethylene glycol,polytetramethylene glycol, and the like.

Of these copolymerization components, at least one member selected fromthe group consisting of isophthalic acid, terephthalic acid, neopentylglycol, 1,4-cyclohexanedimethanol, and diethylene glycol is preferable.Of these copolymerization components, isophthalic acid and terephthalicacid are especially preferable. These copolymerization components may beused solely, or two or more components thereof can also be used.

The polyester (A) can be produced by applying a known method. Forexample, the polyester (A) can be produced by a method in which the diolcomponent and the dicarboxylic acid component as the main components andoptionally the copolymerization component are subjected to anesterification reaction, and subsequently, the obtained reaction productis subjected to a polycondensation reaction to form a polyester. Inaddition, the polyester (A) may also be produced by a method in whichderivatives of these raw material monomers are subjected to an esterinterchange reaction, and subsequently, the obtained reaction product issubjected to a polycondensation reaction to form a polyester.Furthermore, the polyester (A) may also be obtained by a method in whichtwo or more kinds of polyesters are used and melt kneaded within anextruder to achieve an ester interchange reaction (redistributionreaction).

An intrinsic viscosity of the polyester (A) constituting the first layeris in the range of preferably 0.40 to 0.80 dL/g, and more preferably0.45 to 0.75 dL/g. In the case where the intrinsic viscosity of thepolyester (A) constituting the first layer falls outside the foregoingrange, there is a concern that a difference in intrinsic viscosity fromthe polyester (B) constituting the second layer becomes large. As aresult, in the case of forming an alternately laminated structure, thereis a concern that the layer structure is disordered, or though the filmformation can be achieved, the film forming properties are lowered. Inthe case of obtaining the polyester (A) by using two or more kinds ofpolyesters and melt kneading them within an extruder to achieve an esterinterchange reaction, the intrinsic viscosity of each of the polyestersmay fall within the foregoing range.

A melting point of the polyester (A) constituting the first layer ispreferably higher by 10° C. or more, more preferably higher by 15° C. ormore, still more preferably higher by 18° C. or more, and especiallypreferably higher by 20° C. or more than a melting point of thepolyester (B) constituting the second layer as described later. When thedifference in melting point between the polyesters of the both layers isless than the foregoing range, there is a concern that it is difficultto impart a sufficient difference in refractive index to the obtainedlaminated polyester film. As a result, there is a concern thatreflectance properties in a near-infrared wavelength region are notobtained.

In addition, a glass transition temperature of the polyester (A)constituting the first layer is preferably higher than a glasstransition temperature of the polyester (B) constituting the secondlayer.

The first layer of the present invention may contain a small amount ofan additive within the range where the object of the present inventionis not impaired. Examples thereof include additives such as a lubricant,for example, an inactive particle, etc., a coloring agent, for example,a pigment, a dye, etc., a stabilizer, a flame retarder, a foaming agent,and the like. Examples of the lubricant particle include inorganicparticles such as silica, alumina, titanium oxide, calcium carbonate,kaolin, etc., and organic particles such as a deposited particle ofcatalyst residue, silicone, a polystyrene crosslinked material, anacrylic crosslinked material, etc.

Second Layer

In the present invention, the polyester (B) constituting the secondlayer is a polymer containing at least one of an ethylene terephthalatecomponent and an ethylene naphthalene dicarboxylate component.

In addition, a constitution having a protective layer composed of apolymer having a glass transition temperature of 90° C. or higher andhaving a thickness of 5 μm or more and not more than 20 μm on the bothsides of the laminated structure portion (I) in which the first layerand the second layer are alternately laminated is exemplified as onepreferred embodiment of the polyester film of the present invention. Inthe case of such a constitution, examples of the polyester (B)constituting the second layer include (B-i) a polyester containing 50%or more and not more than 95% by mole of an ethylene terephthalatecomponent on the basis of the whole recurring units constituting thepolyester of the second layer, and/or copolymerized polyethyleneterephthalate having a glass transition temperature of lower than 90° C.

Even in the case of using, as the polymer of the second layer, theabove-described copolymerized polyester (B-i) having such acharacteristic feature that a difference in refractive index from thefirst layer is large, and even if the lamination number is decreased, anear-infrared light reflecting performance is easily imparted, whereasat the time of processing into a laminated glass, the film is easilysoftened, in view of the fact that the film has a protective layerhaving such a characteristic feature, the strength of the protectivelayer is kept under a processing condition at the time of processinginto a laminated glass. As a result, flatness of the film can be kept,and a laminated glass with a favorable appearance such that thegeneration of fine irregularities is not perceived can be obtained.

In addition, in the case where the polyester film of the presentinvention is composed of only a laminated structure portion (I) in whichthe first layer and the second layer are alternately laminated, or has aprotective layer having a thickness of less than 5 μm on the both sidesthereof, there is exemplified an embodiment in which the polyester (B)constituting the second layer in the present invention is composed of(B-ii) a polyester having a glass transition temperature of lower than90° C., and a Young's modulus of the film at 20° C. is 5,000 MPa or morein at least one direction of the longitudinal direction and the lateraldirection of the film.

Even when the polyester constituting the second layer has a glasstransition temperature of lower than 90° C. and tends to be softened atthe time of processing into a laminated glass, by simultaneouslyincreasing an area magnification of the stretching to sufficientlyachieve oriented crystallization of the first layer, a degree oforiented crystallization of the first layer is increased, and theYoung's modulus of the film at 20° C. is made to fall within such aregion, whereby the Young's modulus properties of the present inventionat a temperature of 90° C. can be obtained.

As other example of the polyester (B) constituting the second layer, itmay be (B-iii) a polyester having a glass transition temperature of 90°C. or higher, and more preferably, the above-described polyester havinga glass transition temperature of 90° C. or higher may also be apolyester containing 30% by mole or more and not more than 90% by moleof an ethylene naphthalene dicarboxylate component on the basis of thewhole recurring units. In the case of using a polyester having a glasstransition temperature of 90° C. or higher as the polyester (B)constituting the second layer, the Young's modulus properties of thepresent invention at a temperature of 90° C. can be obtained withoutrelying upon the properties and the presence or absence of theprotective layer as the outermost layer, when processed into a laminatedglass, flatness of the film is kept, and a favorable appearance which isfree from the generation of fine irregularities can be obtained.

The polyester (B) constituting the second layer is hereunder describedfor every preferred embodiment.

Embodiment of (B-i)

As an example of the polyester of the second layer in the presentinvention, there is exemplified a polyester containing 50% by mole ormore and not more than 95% by mole of an ethylene terephthalatecomponent, and more preferably copolymerized polyethylene terephthalatehaving 60% by mole or more and not more than 90% by mole of an ethyleneterephthalate component (namely, the copolymerization component iscopolymerized in an amount of preferably 5 to 50% by mole, and morepreferably 10 to 40% by mole) on the basis of the whole recurring unitsconstituting the polyester of the second layer.

In the case where the copolymerization amount is less than the lowerlimit, at the time of film formation, crystallization and orientationare easy to occur, so that a difference in refractive index from thefirst layer is hardly revealed, and the near-infrared light reflectingability is easily lowered. On the other hand, in the case where thecopolymerization amount exceeds the upper limit, at the time of filmformation (in particular, at the time of extrusion), the heat resistanceor film forming properties are easily lowered, and in the case where thecopolymerization component is a component that imparts high refractiveindex properties, a difference in refractive index from the first layeris easy to become small due to an increase of the refractive index. Whenthe copolymerization amount falls within the foregoing range, thedifference in refractive index from the first layer can be sufficientlyensured while keeping favorable heat resistance and film formingproperties, and a sufficient near-infrared light reflecting performancecan be imparted.

Incidentally, for the purposes of ensuring the difference in refractiveindex from the first layer and increasing the reflectance, it ispreferable to control a heat set temperature at the time of filmformation as described later to the melting point or higher of thepolyester (B-i), thereby melting the polyester (B-i) of the second layerwhile maintaining the orientation of the first layer. After stretching,by melting only the second layer to lower the orientation of the secondlayer, the difference in refractive index between the first layer andthe second layer can be made larger. In order to melt only the polyester(B-i) by the heat set treatment, the melting point of the polyester(B-i) is preferably lower by 10° C. or more, and more preferably lowerby 30° C. or more than the melting point of the above-describedpolyester (A).

Examples of the copolymerization component which is preferably used forthe polyester (B-i) include acid components such as aromaticdicarboxylic acids, for example, isophthalic acid,2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid,etc.; aliphatic dicarboxylic acids, for example, adipic acid, azelaicacid, sebacic acid, decanedicarboxylic acid, etc.; alicyclicdicarboxylic acids, for example, cyclohexanedicarboxylic acid; and thelike, as well as glycol components such as aliphatic diols, for example,butanediol, hexanediol, etc.; alicyclic diols, for example,cyclohexanedimethanol; spiro glycol; and the like. Above all,isophthalic acid, 2,6-naphthalenedicarboxylic acid,cyclohexanedimethanol, and spiro glycol are preferable. In the case ofcontaining other copolymerization component than the foregoing, acopolymerization amount thereof is preferably not more than 10% by mole.

In addition, the glass transition temperature of the polyester (B-i) ispreferably not higher than 90° C. By using such a polyester, in the caseof stretching under a stretching condition under which the polyester (A)of the first layer is oriented, the stretching temperature is too highfor the polyester (B-i) of the second layer, and hence, the orientationdoes not proceed, and the difference in refractive index between thefirst layer and the second layer is easily revealed.

The second layer in the present invention may be either amorphous orcrystalline. Here, the term “amorphous” refers to the matter that whenthe biaxially stretched laminated polyester film is subjected to DSCmeasurement at a temperature rise rate of 20° C./min, the melting pointderived from the second layer is not observed. In addition, the term“crystalline” refers to the matter that the melting point derived fromthe second layer is observed in the above-described DSC measurement.

In the case where the polyester of the second layer is the embodiment of(B-i), it is preferable that a protective layer composed of a polymerhaving a glass transition temperature of 90° C. or higher and having athickness of 5 or more and not more than 20 μm is provided on the bothsides of the laminated structure portion (I) in which the first layerand the second layer are alternately laminated. By providing theprotective layer having such a characteristic feature, even in the casewhere a polymer which is easily softened at the time of processing intoa laminated glass is used for the second layer, the strength of theprotective layer is kept under a processing condition at the time ofprocessing into a laminated glass. As a result, flatness of the film canbe kept, and a laminated glass with a favorable appearance such that thegeneration of fine irregularities is not perceived can be obtained.

Embodiment of (B-ii)

In addition, in the case where the polyester film of the presentinvention is composed of only a laminated structure portion (I) in whichthe first layer and the second layer are alternately laminated, or has aprotective layer having a thickness of less than 5 μm on the both sidesthereof, there is exemplified an embodiment in which the polyester (B)constituting the second layer in the present invention is composed of(B-ii) a polyester having a glass transition temperature of lower than90° C., and a Young's modulus of the film at 20° C. is 5,000 MPa or morein at least one direction of the longitudinal direction and the lateraldirection of the film.

Even when the polyester constituting the second layer has a glasstransition temperature of lower than 90° C. and tends to be softened atthe time of processing into a laminated glass, by simultaneouslyincreasing an area magnification of the stretching to sufficientlyachieve oriented crystallization of the first layer, a degree oforiented crystallization of the first layer is increased, and theYoung's modulus of the film at 20° C. is made to fall within such aregion, whereby the Young's modulus properties of the present inventionat a temperature of 90° C. can be obtained. As a result, it becomespossible to keep smoothness of the film at the time of processing into alaminated glass, fine irregularities, wrinkles, or the like are hardlygenerated in the film, and excellent processability into a laminatedglass is revealed.

As an example of the polyester (B-ii) having such a glass transitiontemperature, there is exemplified copolymerized polyethyleneterephthalate containing 50% by mole or more and not more than 97% bymole of an ethylene terephthalate component on the basis of the wholerecurring units constituting the polyester of the second layer andcomposed of 3 to 50% by mole of other copolymerization component. Inaddition, it is more preferable to contain 75 to 97% by mole of theethylene terephthalate component (the proportion of othercopolymerization component is 3 to 25% by mole).

When the proportion of the ethylene terephthalate component is less thanthe lower limit, the film forming properties are easily lowered at thetime of stretching, whereas when the proportion of the ethyleneterephthalate component exceeds the upper limit, there is a concern thata difference in refractive index from the polyester constituting thefirst layer is hardly revealed, and it is difficult to impart asufficient reflectance to the film.

As the copolymerization component other than the ethylene terephthalatecomponent of the polyester (B-ii), one properly selected among thecopolymerization components described for the polyester (B-i) can beused.

Embodiment of (B-iii)

As other embodiment of the polyester (B) constituting the second layerin the present invention, there is exemplified a polyester having aglass transition temperature of 90° C. or higher, more preferably 95° C.or higher, and especially preferably 100° C. or higher.

In view of the fact that the polyester constituting the second layer hassuch a glass transition temperature, the Young's modulus properties ofthe present invention can be obtained under a temperature condition of90° C. without relying upon the properties and the presence or absenceof the protective layer as the outermost layer, and in a process ofprocessing into a laminated glass, fine irregularities, wrinkles, or thelike by means of softening of the polyester film are hardly generated.As a result, smoothness of the film at the time of processing into alaminated glass can be kept, and excellent processability into alaminated glass is revealed.

As the polyester having such a glass transition temperature,specifically, there is exemplified a polyester containing 30% by mole ormore and not more than 90% by mole of an ethylene naphthalenedicarboxylate component on the basis of the whole recurring unitsconstituting the polyester of the second layer.

The lower limit of the proportion of the ethylene naphthalenedicarboxylate component is more preferably 45% by mole, still morepreferably 50% by mole, and especially preferably 55% by mole. Inaddition, the upper limit of the proportion of the ethylene naphthalenedicarboxylate component is more preferably 85% by mole, and especiallypreferably 80% by mole. When the proportion of the ethylene naphthalenedicarboxylate component is the lower limit or more, the polyester has aglass transition temperature of 90° C. or higher. In the case where theproportion of the ethylene naphthalene dicarboxylate component exceedsthe upper limit, there is a concern that a difference in refractiveindex from the refractive index of the first layer is hardly obtained,and it is difficult to obtain sufficient reflectance properties.

As the copolymerization component other than the ethylene naphthalatedicarboxylate constituting the polyester having such a glass transitiontemperature, there can be preferably exemplified acid components such asaromatic carboxylic acids, for example, isophthalic acid, terephthalicacid, orthophthalic acid, biphenyldicarboxylic acid, etc.; aliphaticdicarboxylic acids, for example, succinic acid, adipic acid, azelaicacid, sebacic acid, decanedicarboxylic acid, etc.; and alicyclicdicarboxylic acids, for example, cyclohexanedicarboxylic acid, etc., aswell as glycol components such as aliphatic diols, for example,diethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, neopentyl glycol, etc.; alicyclic diols, for example,1,4-cyclohexanedimethanol, etc.; polyethylene glycol, polytetramethyleneglycol, and the like. In addition, 2,7-naphthalenedicarboxylic acid or1,5-naphthalenedicarboxylic acid may also be used as a secondarycopolymerization component. Of these copolymerization components,terephthalic acid and isophthalic acid are preferable, and terephthalicacid is especially preferable.

Though the upper limit of the glass transition temperature of theabove-described polyester (B-iii) is naturally determined depending uponthe exemplified polyester component and is not particularly limited, ittends to become lower than the glass transition temperature of thepolyester of the first layer.

(Properties of Polyester (B))

An intrinsic viscosity of the polyester (B) constituting the secondlayer is in the range of preferably 0.4 to 1.0 dL/g, more preferably0.45 to 0.95 dL/g, and still more preferably 0.5 to 0.95 dL/g. In thecase where the intrinsic viscosity of the polyester (B) constituting thesecond layer falls outside the foregoing range, there is a concern thata difference in intrinsic viscosity from the polyester (A) constitutingthe first layer becomes large. As a result, in the case of forming analternate laminated structure, there is a concern that the layerstructure is disordered, or though the film formation can be achieved,the film forming properties are lowered.

In the case of obtaining the polyester (B) by using two or more kinds ofpolyesters and melt kneading them within an extruder to achieve an esterinterchange reaction, the intrinsic viscosity of each of the polyestersmay fall within the foregoing range.

In addition, in the case where the intrinsic viscosity is furtherincreased within the forgoing range, a haze value of the film can bemade small. Specifically, so far as the intrinsic viscosity of thepolyester (B) constituting the second layer is in the range of 0.75 to0.95 dL/g, an effect for making the haze value small is easily revealed.

In addition when the polyester (B) constituting the second layer isamorphous, the haze value can be made smaller. The range of thecopolymerization amount at which the polyester (B) is amorphous varieswith the kind of the copolymerization component, and for example, in thecase where the copolymerization component of copolymerized PET isisophthalic acid or a naphthalenedicarboxylic acid, the copolymerizationamount is approximately 30% by mole or more.

The polyester (B) in the present invention can be produced by applying aknown method. For example, the polyester (B) can be produced by a methodin which the acid component and the glycol component as the maincomponents and optionally the copolymerization component are subjectedto an esterification reaction, and subsequently, the obtained reactionproduct is subjected to a polycondensation reaction to form thepolyester. In addition, the polyester (B) may also be produced by amethod in which derivatives of these raw material monomers are subjectedto an ester interchange reaction, and subsequently, the obtainedreaction product is subjected to a polycondensation reaction to form apolyester. Furthermore, the polyester (B) may also be obtained by amethod in which two or more kinds of polyesters are used and meltkneaded within an extruder to achieve an ester interchange reaction(redistribution reaction).

The second layer of the present invention may contain a small amount ofan additive within the range where the object of the present inventionis not impaired. Examples thereof include additives such as a lubricant,for example, an inactive particle, etc., a coloring agent, for example,a pigment, a dye, etc., a stabilizer, a flame retarder, a foaming agent,and the like. Examples of the lubricant particle include inorganicparticles such as silica, alumina, titanium oxide, calcium carbonate,kaolin, etc., and organic particles such as a deposited particle ofcatalyst residue, silicone, a polystyrene crosslinked material, anacrylic crosslinked material, etc.

[Laminated Structure]

The biaxially stretched laminated polyester film of the presentinvention is a laminated film comprising 51 layers or more in total, inwhich the above-described first layer and second layer are alternatelylaminated. By adopting such a lamination number, the selectivereflection by multiple interference can be made large, and a sufficientreflectance can be obtained. In addition, it is preferable that thelamination number is larger because the reflectance properties in anear-infrared wavelength region more increase. From the viewpoint ofproductivity, an upper limit of the lamination number is preferably notmore than 900 layers. In addition, the lower limit of the laminationnumber is more preferably 101 layers, and still more preferably 150layers. When the layer number is less than the lower limit, theselective reflection by multiple interference is small, and a sufficientnear-infrared reflecting performance is not obtained.

[Layer Thickness]

The thickness of each of the first layer and the second layer in thepresent invention is preferably a thickness at which an effect forselectively reflecting a near-infrared light by optical interferencebetween layers.

Here, the reflection wavelength of the laminated film is correspondingto two times of a total of optical thicknesses of the first layer andthe second layer adjacent to each other. Such an optical thickness isexpressed by the product of the refractive index and the thickness ofeach layer, and it is preferable to adjust the thickness of each layerby the refractive index of the resin to be used and the desiredreflection wavelength.

In addition, as described in Radford et al., Reflectivity of IridescentCoextruded Multilayered Plastic Films and Polymer Engineering andScience, Vol. 13, No. 3 (May 1973), in multilayer films utilizingmultiple interference by a quarter wavelength, even in the case where amain reflection peak is not generated in a visible light region, when ahigher order reflection peak is generated in a visible light region,coloration by higher-order reflection may be possibly exhibited.Therefore, it is preferable to adopt an appropriate optical thicknessfor the purpose of eliminating the higher-order reflection.

In multilayer interference films, in the case where a ratio of theoptical thickness of the second layer to the optical thickness of thefirst layer of the main reflection peak is 1.0, among higher-orderpeaks, a second-order peak (one-half wavelength of the main reflectionpeak) and a fourth-order peak (quarter wavelength of the main reflectionpeak) can be removed.

As an example in which an appropriate optical thickness for eliminatingthe higher-order reflection is taken into consideration, in the casewhere polyethylene-2,6-naphthalenedicarboxylate (hereinafter referred toas “PEN”) is used for the first layer, copolymerized polyethyleneterephthalate having 12% by mole of isophthalic acid copolymerizedtherewith (hereinafter referred to as “IA12PET”) is used for the secondlayer, and a wavelength of 800 to 1,200 nm is subjected to primaryreflection, the thickness of each layer is described. In general, arefractive index of PEN in the stretching direction is 1.74 to 1.78, anda refractive index of IA12PET in the stretching direction is about 1.58to 1.65, values of which are, however, variable depending upon the filmforming conditions of the film, and hence, the thickness of each layerof the first layer is preferably in the range of 0.1 μm or more and notmore than 0.2 μl. In an example of the combination of PEN and IA12PET,when each layer of the first layer has a thickness of this range, it ispossible to selectively reflect and shield the light in a near-infraredregion.

In the range where the thickness of the first layer is thinner than thelower limit, the reflected light is in a visible light region, so thatthere is a concern that the film is colored to lower the visibility. Onthe other hand, when the thickness of the first layer exceeds the upperlimit, a third order peak (one-third of the main reflection peak) isgenerated in a visible light region by optical interference betweenlayers, and therefore, there is a concern that coloration is caused, sothat the transparency is impaired.

In addition, in an example of the combination of PEN and IA12PET, inorder to obtain an effect for selectively reflecting a near-infraredlight by optical interference between layers, the thickness of eachlayer of the second layer is preferably in the range of 0.09 μm or moreand not more than 0.22 μm, and more preferably 0.10 μm or more and notmore than 0.20 μm. When each layer of the second layer has a thicknessof this range, it is possible to selectively reflect and shield thelight in a near-infrared region. In the range where the thickness of thesecond layer is thinner than the lower limit, the reflected light is ina visible light region, so that there is a concern that the film iscolored to lower the visibility. On the other hand, when the thicknessof the second layer exceeds the upper limit, a third-order peak isgenerated in a visible light region by optical interference betweenlayers, and therefore, there is a concern that coloration is caused, sothat the transparency is impaired.

In the case of the laminated polyester film of the present invention, bytaking the relation of optical thicknesses and the refractive index ofeach layer as described above into consideration and more increasing thecombination such that a ratio (thickness ratio) of the thickness of thesecond layer to the thickness of the first layer adjacent to each otherfalls within the range of 0.9 to 1.1, it is possible to decreasehigher-order peaks generated in the visible light region, and it is alsopossible to make the average reflectance in the visible light regionsmaller.

This relation may be enough to be satisfied in the majority of thelayers of the laminated film and may be enough to be satisfied in 70% ormore, preferably 80% or more, more preferably 90% or more, andespecially preferably 95% or more of the total layer number of thelaminated structure portion.

As for the thickness of each layer, in order to enhance the reflectancein a wavelength region of 800 to 1,200 nm, it is preferable tocontinuously change a ratio of the maximum thickness to the minimumthickness (maximum/minimum) in the first layer between 1.2 and 1.8.

In addition, as for the thickness of each layer of the second layer, inorder to enhance the reflectance in a wavelength region of 800 to 1,200nm, it is preferable to continuously change a ratio of the maximumthickness to the minimum thickness (maximum/minimum) between 1.2 and1.6.

[Protective Layer]

It is preferable that the biaxially stretched laminated polyester filmof the present invention has a protective layer composed of a polymerhaving a glass transition temperature of 90° C. or higher, andpreferably 110° C. or higher and having a thickness of 5 μm or more andnot more than 20 μm, preferably 7 μm or more and not more than 15 μm,and more preferably 7 μm or more and not more than 13 μm on the bothsides of the laminated structure portion thereof. According to this, thestrength of the protective layer is kept even under a processingtemperature condition at the time of processing into a laminated glass,and the 90° C. Young's modulus properties of the present invention canbe obtained. As a result, flatness of the film is kept at the time ofprocessing into a laminated glass, and a laminated glass with afavorable appearance such that the generation of fine irregularities isnot perceived is obtained.

In the case where the glass transition temperature of the polymer of theprotective layer is lower than 90° C., or in the case where thethickness of the protective layer is less than 5 μm, there is a concernthat when processed into a laminated glass, the effect for inhibitingfine irregularities is decreased depending upon the polyesterconstitution of the second layer.

Meanwhile, in the case where the thickness of the protective layerexceeds 20 μm, there is a concern that not only the effect forinhibiting the generation of fine irregularities does not change fromthat in the case where the thickness of the protective layer is thinnerthan the former, but when molded into a curved laminated glass, thefollow-up properties toward the curved proportion are lowered.

Examples of the polymer having a glass transition temperature of 90° C.or higher, which is preferably used for the protective layer, includepolyethylene naphthalate, polycarbonate, polystyrene, polymethylmethacrylate, polyphenylene sulfide, polyether sulfone, polyphenyleneoxide, and the like. As for a method of laminating the protective layer,the laminated structure portion and the protective layer may besimultaneously fabricated by means of co-extrusion, or only theprotective layer may be stuck later. Above all, it is preferable thatpolyethylene-2,6-naphthalate that is a polymer of the first layer isused for the protective layer, and the protective layer and thelaminated structure portion are simultaneously fabricated by aco-extrusion method.

Incidentally, in the case where the polyester of the second layer is theembodiment of (B-ii) or (B-iii), even when such a structure of theprotective layer is not adopted, the object of the present invention canbe achieved. As for the structure other than the above-describedprotective layer, specifically, the protective layer may not be used, orthe protective layer may be one having a thickness of less than 5 μm.

[Difference in Refractive Index]

A difference in refractive index between the first layer and the secondlayer is preferably 0.09 or more, more preferably 0.11 or more, andstill more preferably 0.13 or more in all of the longitudinal direction(longer direction, film forming direction, or MD direction) and thelateral direction (width direction, perpendicular direction to the filmforming direction, or TD direction). When the difference in refractiveindex falls within such a range, the reflection properties can beefficiently increased, and therefore, a high reflectance can be obtainedin a smaller lamination number.

In the biaxially stretched laminated polyester film of the presentinvention, the above-described polyester is adopted for the first layerand the second layer, and therefore, the above-described difference inrefractive index can be easily attained by choosing a film formingcondition (stretching condition or heat set condition) as describedlater.

[Reflectance Properties]

The biaxially stretched laminated polyester film of the presentinvention has not only an average reflectance of not more than 25%within a wavelength range of 400 to 750 nm but an average reflectance of50% or more within a wavelength range of 800 to 1,200 nm.

In view of the facts that the average reflectance in a visible lightwavelength region is low, the transmittance in such a wavelength regionis high, and at the same time, the average reflectance in anear-infrared wavelength region is high, for example, when used as anear-infrared light shielding film of a laminated glass for a windowsuch as a building window, an automotive window, etc., it is possible toachieve high visibility and high transparency and also to efficientlyincrease a near-infrared light shielding performance.

The average reflectance within a wavelength region of 400 to 750 nm ismore preferably not more than 20%. In view of the fact that thereflectance in a visible light wavelength region is small, thetransparency becomes higher, and the visibility increases. In addition,the average reflectance within a wavelength range of 800 to 1,200 nm ismore preferably 55% or more, and still more preferably 60% or more. Whenthe reflectance in this wavelength region becomes higher, the heat rayshielding effect in a near-infrared wavelength region increases, and asunlight transmittance is lowered.

[Young's Modulus Properties of Film at 90° C.]

In the biaxially stretched multilayer polyester film of the presentinvention, a Young's modulus of the film at 90° C. is 2,400 MPa or more,preferably 2,600 MPa or more, and more preferably 2,700 MPa or more inat least one direction of the longitudinal direction and the lateraldirection of the film. What the Young's modulus at 90° C. is less thanthe foregoing range in the both directions of the longitudinal directionand the lateral direction of the film is not preferable because whenprocessed into a laminated glass, the film is deformed, fineirregularities or wrinkles are generated in the film, so that thesmoothness of the film is lowered, and the processability into alaminated glass is lowered. In addition, it is more preferable that theYoung's modulus of the film at 90° C. falls within the foregoing rangein both the longitudinal direction and the lateral direction of thefilm.

In order to obtain the Young's modulus properties at 90° C., there isexemplified a method in which polyethylene-2,6-naphthalenedicarboxylateis used as the polyester (A) constituting the first layer, furthermore,the polyester of any one of the embodiments is used as the polyester (B)constituting the second layer, and moreover, a protective layer composedof a polymer having a glass transition temperature of 90° C. or higherand having a thickness of 5 μm or more and not more than 20 μm is usedaccording to the embodiment of the polyester (B).

In view of the fact that a protective layer having such properties isprovided on the both sides of the laminated structure portion (I), evenwhen the polyester of the second layer is softened under an atmosphereof 90° C., the protective layer has sufficient rigidity, so that theprocessability into a laminated glass can be increased.

In addition, by using polyethylene-2,6-naphthalenedicarboxylate for thefirst layer, furthermore, using a polyester having a glass transitiontemperature (Tg) of lower than 90° C. as the polyester (B) constitutingthe second layer, and simultaneously increasing an area magnification ofthe stretching to sufficiently achieve oriented crystallization of thefirst layer, though the second layer itself is softened under anatmosphere at 90° C., and the Young's modulus at 90° C. tends to belowered, the first layer acts as a rigid layer of the laminatedpolyester film, and such Young's modulus properties can be obtained.

In addition, by using a polyester having a glass transition temperatureof 90° C. or higher as the polyester (B) constituting the second layer,sufficient rigidity at 90° C. is obtained, at the time of processinginto a laminated glass, processing can be achieved without causingsoftening of the second layer, and the processability into a laminatedglass can be increased.

[Young's Modulus of Film at 20° C.]

In the biaxially stretched laminated polyester film of the presentinvention, in the case where the polyester constituting the second layeris the polyester (B-ii) having a glass transition temperature of lowerthan 90° C., at the same time, it is preferable that the Young's modulusof the film at 20° C. is 5,000 MPa or more in at least one direction ofthe longitudinal direction and the lateral direction of the film, and itis more preferable that the Young's modulus of the film at 20° C. is5,000 MPa or more in both the longitudinal direction and the lateraldirection of the film. Here, in the case where the Young's modulusproperties at 20° C. are satisfied in only one direction, it ispreferable that such a direction is the same direction as a direction inwhich the Young's modulus at 90° C. is higher.

Even when the polyester constituting the second layer is a polymerhaving a glass transition temperature of lower than 90° C. and beingeasily softened at the time of processing into a laminated glass, bysimultaneously increasing an area magnification of the stretching tosufficiently achieve oriented crystallization of the first layer, adegree of oriented crystallization of the first layer is increased, andthe Young's modulus of the film at 20° C. is made to fall within such aregion, whereby the Young's modulus properties of the present inventionat a temperature of 90° C. can be obtained. The area magnification forobtaining such Young's modulus properties is preferably 17 times ormore, more preferably 18 times or more, and especially preferably 20times or more.

In addition, even in the case where the polyester constituting thesecond layer is a polyester having a glass transition temperature of 90°C. or higher, the stretch ratio can be increased, and furthermore, theYoung's moduli at 20° C. and 90° C. can be enhanced.

[Visible Light Transmittance]

In the biaxially stretched laminated polyester film of the presentinvention, a visible light transmittance within a wavelength range of400 to 750 nm is preferably 75% or more, more preferably 80% or more,and especially preferably 85% or more. The visible light transmittancecan be determined according to the regulations of JIS-R3106. When thefilm of the present invention is provided with such visible lighttransmittance properties, when used for a laminated glass for a windowsuch as a building window, an automotive window, etc., transparency witha high degree is obtained, and high visibility is obtained.

[Sunlight Transmittance]

In the present invention, in the biaxially stretched laminated polyesterfilm, when used for a laminated glass for a window such as a buildingwindow, an automotive window, etc., in order to obtain near-infraredlight shielding properties with a high degree, a solar transmittance ofsunlight as regulated in JIS-R3106 is preferably not more than 80%, morepreferably not more than 75%, and especially preferably not more than70%. Such sunlight transmittance properties are obtained by increasing areflecting performance in a wavelength region of 800 to 1,200 nm whileincreasing the transmittance in a visible region as described above.

[Thermal Shrinkage Properties]

In the biaxially stretched laminated polyester film of the presentinvention, in the case where it is used for an application to alaminated glass having a curved surface, a thermal shrinkage at 120° C.for 30 minutes is preferably 0.6 to 3.0%, and more preferably 0.9 to3.0%; in both the longitudinal direction and the lateral direction ofthe film. When the heat shrinkage is less than the lower limit, there isa concern that when processing into a laminated glass by sandwiching thefilm between laminated glasses having a curved surface and sticking themto each other by a heating treatment is applied, there is a concern thatthe film cannot sufficiently shrink in conformity with the curved shapeof glass depending upon the curved shape, and wrinkles are generated. Onthe other hand, when the thermal shrinkage exceeds the upper limit,there is a concern that the shrinkage of the film at the time ofprocessing into a laminated glass becomes large, and the reflectionwavelength changes.

In the film production step, such thermal shrinkage properties can beobtained by controlling a heat set temperature to 150 to 210° C., andthe heat set temperature is more preferably in the range of 150 to 200°C.

[Lubricant]

From the viewpoint of maintaining high transparency in a visible lightwavelength region, it is preferable that the biaxially stretchedlaminated polyester film of the present invention does not containinactive particles in the film. However, for the purpose of preventingfine scratches in the production step or enhancing wind-up properties ofthe film, it is also tolerable to contain a small amount of inactiveparticles. In that case, the inactive particles may be contained ineither one or both of the first layer and the second layer. As theinactive particles, for example, those having an average particlediameter of 0.01 μm to 2 more preferably 0.05 to 1 μm, and especiallypreferably 0.1 to 0.3 μm may be used. In the case of using inactiveparticles, the inactive particles can be blended in an amount of, forexample, 0.001% by weight to 0.01% by weight on the basis of the weightof the laminated film.

In the case of blending inactive particles, when the average particlediameter of the inactive particles is smaller than the lower limit, orthe content thereof is less than the lower limit, an effect forenhancing the wind-up properties of the film is easy to becomeinsufficient. On the other hand, when the content of the inactiveparticles exceeds the upper limit, or the average particle diameterthereof exceeds the upper limit, the transparency tends to be lowered.

Examples of the inactive particles include inorganic inactive particlessuch as silica, alumina, calcium carbonate, calcium phosphate, kaolin,talc, etc.; and organic inactive particles such as silicone, crosslinkedpolystyrene, and a styrene-divinylbenzene copolymer.

These inactive particles are preferably granular particles having alonger diameter-to-shorter diameter ratio of not more than 1.2, and morepreferably not more than 1.1 (hereinafter often referred to as “pearlyparticles”) from the viewpoint of maintaining the lubricity andtransparency of the film as far as possible. In addition, it ispreferable that the particle size distribution of these inactiveparticles is sharp.

[Ultraviolet Light Absorber]

It is preferable that the biaxially stretched laminated polyester filmof the present invention has at least one layer containing anultraviolet light absorber.

The ultraviolet light absorber which is used in the present invention isan ultraviolet light absorber having an extinction coefficient E at awavelength of 380 nm of preferably 2 or more, and more preferably 3 ormore. The extinction coefficient as referred to herein is expressed bythe following equation (1), and it is an extinction coefficient obtainedby measuring an absorbance of the ultraviolet light absorber dissolvedin tetrahydrofuran and calculating from a concentration value accordingto the Lambert-Beer equation.

∈=A/(c×b)  (1)

(In the foregoing equation (1), 6 represents an extinction coefficient;A represents an absorbance; c represents a concentration (g/L); and brepresents an optical path length (cm) in the sample.)

By using the ultraviolet light absorber having such light absorptionproperties, nevertheless the laminated polyester film containing apolyethylene-2,6-naphthalenedicarboxylate layer having relatively lowultraviolet light durability, it is possible to impart high ultravioletlight durability such that the laminated polyester film can be used forheat ray shielding applications to windows of vehicles or buildings, orthe like.

Examples of the ultraviolet light absorber include a triazine-basedultraviolet light absorber, a benzotriazole-based ultraviolet lightabsorber, a benzophenone-based ultraviolet light absorber, abenzoxazinone-based ultraviolet light absorber, a cyano acrylate-basedultraviolet light absorber, and a salicylate-based ultraviolet lightabsorber. Though a triazine-based ultraviolet light absorber or abenzotriazole-based ultraviolet light absorber is preferably used, allof these ultraviolet light absorbers are not always satisfactory withrespect to the above-described light absorption properties, and it isnecessary to use an ultraviolet light absorber selected among theseultraviolet light absorbers.

Specifically, examples of the ultraviolet light absorber satisfied withthe properties such that the extinction coefficient ∈ at a wavelength of380 nm is 2 or more include

-   2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine,-   2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol,-   2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol,    octyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propipnate,-   2-ethylhexyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate,-   2-(2H-benzotriazol-2-yl)-4,6-bis(1-ethyl-1-phenylethyl)phenol,-   2-(5-chloro-2H-benzotriazol-2-yl)-6-(1,1-dimethylethyl)-4-methyl,-   2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-1,1,3,3-tetra    methylbutyl)phenol),-   2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol,-   2,4-bis(2-hydroxy-4-butyloxyphenyl)-6-(2,4-bis-butyloxyphenyl)-1,3,5-triazine,    benzenepropanoic acid,-   3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-C7-9    branched and chain alkyl esters,-   2-(2-hydroxy-5-tert-methylphenyl)-2H-benzotriazole,-   2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol,-   2,2′-dihydroxy-4-methoxybenzophenone,-   2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(octyloxy)phenol,    and-   2-(2′-hydroxy-5′-octylphenyl)benzotriazole.

A concentration of the ultraviolet light absorber in the layercontaining an ultraviolet light absorber is, for example, 0.1% by weightor more, preferably 1 to 80% by weight, more preferably 1 to 50% byweight, and still more preferably 5 to 20% by weight on the basis of theweight of the layer. When the content of the ultraviolet light absorberis less than the lower limit, there is a concern that a sufficienteffect for absorbing an ultraviolet light is not obtained.

In the case where the biaxially stretched laminated polyester film ofthe present invention contains such an ultraviolet light absorber, anaverage light transmittance of the film within a wavelength range of 300nm or more and less than 400 nm is preferably not more than 10%, andmore preferably not more than 5%.

In the case of containing the ultraviolet light absorber in any one ofthe layers of the biaxially stretched laminated polyester film of thepresent invention, it is preferable that the ultraviolet light absorberis contained in at least the outermost layer, and in the case ofproviding a protective layer on the both sides of the multilayerlaminated portion, it is preferable that the ultraviolet light absorberis contained in at least the protective layer.

Besides, there may also be adopted an embodiment in which the layercontaining an ultraviolet light absorber is provided on the outermostlayer of the laminated film by a co-extrusion method; or an embodimentin which a coating layer is provided by a method such as coating, etc.,and an ultraviolet light absorber is contained in such a coating layer.

In providing such a layer on the outermost layer of the laminated film,it is preferable to stick the ultraviolet light absorber onto the filmby using a binder resin. Examples of the binder resin include apolyester resin, an acrylic resin, an acrylic silicon resin, a urethaneresin, a fluorine resin, a silicon resin, a melamine-based resin, acellulose resin, and a polyamide resin. Of these binder resins, anacrylic resin, an acrylic silicon resin, a urethane resin, a siliconresin, and a fluorine resin are preferable because of excellent lightstability; and a polyester resin is easily laminated in the alternatelylaminated portion between the first layer and the second layer by aco-extrusion method or the like.

In addition, as described later, in the case of being used for alaminated glass, it is more preferable to contain the ultraviolet lightabsorber in a resin layer that allows the glass sheet and the film toadhere to each other, such as polyvinyl butyral as described later. Inthis way, it is preferable to shield an ultraviolet light at a stagebefore the ultraviolet light reaches thepolyethylene-2,6-naphthalenedicarboxylate layer, and it is preferable tocontain the ultraviolet light absorber in the layer positioned outside.

In addition, a quencher or a light stabilizer such as HALS may be usedjointly together with the ultraviolet light absorber.

[Coating Layer]

In the biaxially stretched laminated polyester film of the presentinvention, in order to inhibit a phenomenon in which when processed intoa laminated glass, an image reflected on the laminated glass is seendistorted, it is preferable that a coating layer (hereinafter oftenreferred to as “coating film” or “easily adhesive layer”) having arefractive index of 1.60 to 1.63 and a thickness of 0.05 to 0.20 μm, andpreferably 0.08 to 0.12 μm is provided on at least one surface of theabove-described laminated polyester film. In the case where therefractive index or thickness of the coating layer falls outside theforegoing range, there is a concern that the phenomenon in which whenprocessed into a laminated glass, an image reflected on the laminatedglass is seen distorted cannot be sufficiently decreased. In addition,when the coating layer becomes thick, the haze tends to become high, andwhen the thickness of the coating layer exceeds the upper limit, thereis a concern that a lowering of the visibility to be caused due to thediffused light is accompanied.

The constitution of the coating layer is arbitrary so long as it has theabove-described refractive index properties. For example, a combined useof, as polymer binder components, a polyester C containing a diolcomponent having a specified fluorene structure and having a glasstransition temperature of 90 to 135° C. and a polyester D having a glasstransition temperature of 25° C. or higher and not higher than 80° C. ispreferable because it is easy to take a balance between the conformationin refractive index of the coating layer and the film forming propertiesby an in-line coating method to be generally adopted at the time offorming a coating layer.

(Polyester C)

The polyester C constituting the coating layer is preferably a polyestercontaining, as a diol component, a component having a fluorene structurerepresented by the following formula (I) in an amount of 20 to 80% bymole relative to the whole diol components and having a glass transitiontemperature of 90 to 135° C.

(R₁ represents an alkylene group having 2 to 4 carbon atoms; and R₂, R₃,R₄, and R₅ may be the same as or different from each other and eachrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, an arylgroup, or an aralkyl group.)

When the polyester C obtained by using a component having such afluorene structure as one of the diol components is used as the polymerbinder component of the coating layer, it is possible to easily adjustthe refractive index of the coating layer to a range of 1.60 to 1.63.

Examples of the diol component having a fluorene structure include9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-methylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-dimethylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-ethylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-diethylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-propylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-dipropylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-isopropylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-diisopropylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-n-butylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-di-n-butylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-isobutylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-diisobutylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-(1-methylpropyl)phenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-bis(1-methylpropyl)phenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-diphenylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3-benzylphenyl]fluorene,9,9-bis[4-(2-hydroxyethoxy)-3,5-dibenzylphenyl]fluorene,9,9-bis[4-(3-hydroxypropoxy)phenyl]fluorene, and9,9-bis[4-(4-hydroxybutoxy)phenyl]fluorene. Above all,9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is especially preferable.

The lower limit value of the content of the diol component having such afluorene structure is preferably 25% by mole, and more preferably 30% bymole. On the other hand, the upper limit value thereof is preferably 75%by mole, and more preferably 70% by mole.

In the case where the content of the diol component having such afluorene structure is less than the lower limit value, there is aconcern that an effect for enhancing the refractive index is small, andit is difficult to obtain the coating layer whose refractive index fallswithin the foregoing range. On the other hand, in the case where thecontent of the diol component exceeds the upper limit value, whenprocessed into a laminated glass, there is a concern that not only theadhesiveness to the resin layer such as an ethylene-vinyl acetatecopolymer, polyvinyl butyral, an ionomer resin, etc. is lowered, but thefilm surface becomes rough, or the blocking resistance is lowered.

As other diol component constituting the polyester C, there isexemplified ethylene glycol. It is preferable that ethylene glycol iscontained in an amount ranging from 20 to 80% by mole relative to thewhole diol components of the polyester C. The lower limit value of thecontent of such ethylene glycol is preferably 35% by mole, and morepreferably 40% by mole. In addition, the upper limit value of thecontent of ethylene glycol is preferably 75% by mole, and morepreferably 65% by mole. In the case where the content of ethylene glycolis less than the lower limit value, there is a concern that the blockingresistance of the film is lowered. On the other hand, in the case wherethe content of ethylene glycol exceeds the upper limit value, thecontent of the above-described diol component having a fluorenestructure becomes less than the lower limit value.

Examples of a diol component other than the diol component having afluorene structure and ethylene glycol constituting the polyester Cinclude 1,4-butanediol, 1,4-cyclohexanedimethanol, bisphenol A, and thelike. In addition, diethylene glycol which is not added as the monomercomponent but is generated in the polymerization process may becontained, too. A lower limit value of the content of such other diolcomponent is preferably 5% by mole. On the other hand, an upper limitvalue of the content of other diol component is preferably 40% by mole,more preferably 20% by mole, and still more preferably 10% by mole.

It is preferable that a component derived from a naphthalenedicarboxylicacid, especially a component derived from 2,6-naphthalenedicarboxylicacid, is contained in an amount of 40 to 99% by mole relative to thewhole dicarboxylic acid components of the polyester C as thedicarboxylic acid component which is used for the polyester C. By usinga naphthalenedicarboxylic acid as the dicarboxylic acid component, therefractive index of the polyester C can be increased, and the refractiveindex of the coating layer can be easily made to fall within theforegoing range.

The lower limit value of the content of the component derived from anaphthalenedicarboxylic acid is more preferably 50% by mole, still morepreferably 60% by mole, and especially preferably 70% by mole. Inaddition, the upper limit value of the proportion of the componentderived from a naphthalenedicarboxylic acid is more preferably 95% bymole.

It is preferable that 0.1 to 5% by mole of a component derived from anaromatic dicarboxylic acid having a sulfonic acid salt group and 0 to60% by mole of other aromatic dicarboxylic acid are contained as otherdicarboxylic acid component which is used for the polyester C relativeto the whole dicarboxylic acid components of the polyester C. When thearomatic dicarboxylic acid having a sulfonic acid salt group iscontained as the copolymerization component, it becomes easy towater-disperse the polyester C.

The lower limit value of the content of the aromatic dicarboxylic acidhaving a sulfonic acid salt group is more preferably 1% by mole, stillmore preferably 2% by mole, and especially preferably 3% by mole. In thecase where the content of the aromatic dicarboxylic acid having asulfonic acid salt group is less than the lower limit value, there is aconcern that the hydrophilicity of the polyester C is lowered, and thewater-dispersing is not sufficient. On the other hand, when the contentof the aromatic dicarboxylic acid having a sulfonic acid salt groupexceeds the upper limit value, the hydrophilicity of the film becomeslarge, and as a result, there is a concern that the blocking resistanceis lowered.

Preferred examples of such an aromatic dicarboxylic acid having asulfonic acid salt group include 5-sodium sulfoisophthalic acid,5-potassium sulfoisophthalic acid, 5-lithium sulfoisophthalic acid, and5-phosphonium sulfoisophthalic acid. In order to enhance the waterdispersibility, 5-sodium sulfoisophthalic acid, 5-potassiumsulfoisophthalic acid, and 5-lithium sulfoisophthalic acid are morepreferable. Above all, 5-sodium sulfoisophthalic acid is the mostpreferable.

As for the dicarboxylic acid component of the polyester C, it ispreferable that a component derived from a naphthalenedicarboxylic acidis contained, from the viewpoint of refractive index properties, andfurthermore, a component derived from an aromatic dicarboxylic acidhaving a sulfonic acid salt group is used from the standpoint ofeasiness of water-dispersing the polyester C. However, other aromaticdicarboxylic acid may also be used together with these components.Examples of other aromatic dicarboxylic acid include isophthalic acid,terephthalic acid, and biphenyldicarboxylic acid. Of these, isophthalicacid is especially preferable.

A lower limit value of the proportion of other aromatic dicarboxylicacid is preferably 3% by mole, and more preferably 5% by mole. Inaddition, an upper limit value of the proportion of other aromaticdicarboxylic acid is preferably 50% by mole, more preferably 40% bymole, and still more preferably 30% by mole.

The glass transition temperature of the polyester C is 90 to 135° C.,and more preferably 100 to 130° C. Such a glass transition temperaturecan be easily attained by allowing the constituent components of thepolyester C and the content thereof to fall within the above-describedpreferred ranges.

A refractive index of the polyester C is preferably more than 1.60 andnot more than 1.65, and more preferably 1.63 to 1.65. Such refractiveindex properties can be attained by using a diol component having afluorene structure as the diol component of the polyester C, andfurthermore, can be more easily attained by using jointly anaphthalenedicarboxylic acid component as the dicarboxylic acidcomponent.

An intrinsic viscosity of the polyester C is preferably 0.2 to 0.8 dL/g.Such an intrinsic viscosity is a value measured at 35° C. by usingorthochlorophenol.

(Polyester D)

In the coating layer in the present invention, it is preferable to usejointly a polyester D having a glass transition temperature of 25 to 80°C. in addition to the above-described polyester C.

When the polyester D having a glass transition temperature fallingwithin such a temperature range is used together with the polyester C,the coating layer is coated on the laminated polyester film, thereafter,the coating layer becomes sufficiently softened at a temperature of thestep of applying a stretching treatment to the film, and the fragilenessof the polyester C is improved, whereby the film forming properties ofthe coating layer can be increased. Then, by increasing the film formingproperties of the coating layer, the surface of the coating layerbecomes smooth, so that the deterioration of a haze value to be causeddue to the coating layer can be minimized.

The lower limit value of the glass transition temperature of thepolyester D is preferably 50° C., and more preferably 60° C. Inaddition, the upper limit value of the glass transition temperature ofthe polyester D is preferably 75° C. In the case where the glasstransition temperature of the polyester D is lower than the lower limitvalue, there is a concern that the solvent resistance of the coatinglayer is lowered due to the polyester C. On the other hand, when theglass transition temperature of the polyester D exceeds the upper limitvalue, an effect for increasing the film forming properties of thecoating layer is not revealed.

Examples of the dicarboxylic acid component which is used for thepolyester D include terephthalic acid, isophthalic acid, phthalic acid,adipic acid, sebacic acid, 5-Na sulfoisophthalic acid, and the like.Above all, terephthalic acid and isophthalic acid are preferable.

In addition, examples of the diol component which is used for thepolyester D include ethylene glycol, diethylene glycol, neopentylglycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, analkylene oxide adduct of bisphenol A, and the like. Besides, apolyhydroxy compound such as glycerin, trimethylolpropane, etc. may beused in a small amount range. Besides, among the whole dicarboxylic acidcomponents of the polyester D, a naphthalenedicarboxylic acid componentor the like may be used in a small amount, for example, within a rangeof not more than 20% by mole.

Of these, as the especially preferred polyester 3D, there is exemplifieda copolymerized polyester containing 90% by mole or more of terephthalicacid relative to the whole dicarboxylic acid components of the polyesterD and ethylene glycol and bisphenol A as the diol component, and byadjusting a proportion of ethylene glycol and bisphenol A, the glasstransition temperature of the polyester D can be adjusted.

A refractive index of the polyester D is preferably 1.50 to 1.59, andmore preferably 1.55 to 1.58. In addition, an intrinsic viscosity of thepolyester D is preferably 0.2 to 0.8 dL/g.

(Content of Polyester C and Polyester ID)

A total content of the polyester C and the polyester D is preferably 50to 100% by weight, more preferably 60 to 97% by weight, and still morepreferably 60 to 95% by weight on the basis of the weight of the coatinglayer. When the content of the polyester C and the polyester D occupyingin the coating layer falls within the foregoing range, it is possible tomake both the refractive index properties and the film formingproperties of the coating layer favorable.

In addition, the content of the polyester C is preferably 40 to 80% byweight, and more preferably 45 to 75% by weight on the basis of thetotal amount of the polyester C and the polyester D. When the content ofthe polyester C falls within the foregoing range, it is possible tosimultaneously enhance the film forming properties in the filmstretching step while increasing the refractive index properties of thecoating layer. On the other hand, in the case where the content of thepolyester C is less than the lower limit value, there is a concern thatthe refractive index of the coating layer cannot be sufficientlyincreased. On the other hand, in the case where the content of thepolyester C exceeds the upper limit value, not only there is a concernthat an enhancement of the film forming properties in the filmstretching step by the polyester D is not sufficient, breakage isgenerated in the coating layer to cause surface scattering, and the hazevalue increases due to the coating layer, but there is a concern thatwhen processed into a laminated glass, the adhesion to the resin layerbecomes poor.

(Other Polymer Binder Component)

As other polymer binder constituting the coating layer, an acrylicresin, a urethane resin, and a modified material thereof, and the likemay be further added as the need arises. By using jointly a small amountof such a resin in addition to the polyesters C and D, it is possible toincrease the adhesiveness to the resin layer which is used for thelaminated glass in addition to the refractive index properties. In thecase of using other polymer binder component than the polyesters C andD, its content is preferably not more than 40% by weight, morepreferably not more than 30% by weight, and still more preferably 1 to20% by weight on the basis of the weight of the coating layer.

(Surfactant)

In the coating layer in the present invention, it is preferable tofurther contain a surfactant. In the case of using a surfactant, itscontent is in the range of preferably 0.1 to 10% by weight, andespecially preferably 0.5 to 7% by weight on the basis of the weight ofthe coating layer. By containing the surfactant within the foregoingrange, the water dispersibility of the polyester C can be increased, andthe particle diameter of the polyester C in the aqueous coating solutionbecomes small to further increase the flatness of the surface of thecoating layer, and therefore, the haze value can be made more favorable.

(Particle)

In the coating layer in the present invention, in the case of processinginto a laminated glass and being used as am automotive windshield, fromthe viewpoint of increasing the visibility, the content of particles inthe coating layer is preferably not more than 1% by weight on the basisof the weight of the coating layer. In addition, the content of theparticles is more preferably 0.001 to 0.8% by weight, and still morepreferably 0.1 to 0.5% by weight. The particles in the coating layer areadded in an extremely small amount for the purpose of impartingslipperiness, and by controlling the content of the particles to theforegoing range, the deterioration of the haze value to be caused due tothe coating layer can be decreased, and the haze value of the whole ofthe film can be decreased.

In the present invention, so long as a high refractive index of thecoating layer is attained by using the polyester C as the polymer bindercomponent, it becomes unnecessary to realize a high refractive index ofthe coating layer due to the particles, and therefore, the content ofthe particles can be minimized within the range where the slipperinessis not impaired.

An average primary particle diameter of such particles is preferably 5to 200 nm. When the average primary particle diameter of the particlesexceeds 200 nm, there is a concern that optical scattering is generated,and the transparency of the coating layer is lowered. On the other hand,when the average primary particle diameter of the particles is less than5 nm, there is a concern that coagulation among the particles increases,and a secondary particle diameter becomes large, so that opticalscattering is generated, and the transparency of the coating layer islowered.

The kind of the particles is not particularly limited, and examples ofthe particles which can be used include inorganic particles such ascalcium carbonate, magnesium carbonate, calcium oxide, zinc oxide,magnesium oxide, silicon oxide, sodium silicate, aluminum hydroxide,iron oxide, zirconium oxide, barium sulfate, titanium oxide, tin oxide,antimony trioxide, carbon black, molybdenum disulfide, etc.; and organicparticles such as an acrylic crosslinked polymer, a styrene-basedcrosslinked polymer, a silicone resin, a fluorine resin, abenzoguanamine resin, a phenol resin, a nylon resin, etc.

[Formation of Coating Layer]

The coating layer in the present invention can be preferably formed bycoating the above-described polyesters C and D in a water dispersionstate, or if desired, a mixture thereof with other coating layercomponent to be used jointly in an aqueous coating solution state, on atleast one surface, and preferably both surfaces of the laminatedpolyester film.

The polyester water dispersion is preferably produced by the followingmethod. That is, the polyesters C and D are dissolved in a hydrophilicorganic solvent not only having a solubility in one liter of water of 20g or more at 20° C. but having a boiling point of not higher than 100°C., or capable of causing azeotropy with water at not higher than 100°C. Examples of the organic solvent having such a solubility and capableof dissolving a polyester therein include dioxane, acetone,tetrahydrofuran, and methyl ethyl ketone. By further adding a smallamount of a surfactant to such a solution, it is also possible toenhance wettability of the obtained aqueous coating solution with thefilm.

To the organic solution having the polyesters C and D dissolved therein,water is then added under stirring, and preferably under high-speedstirring at an elevated temperature, thereby forming a bluish white tomilky white dispersion. In addition, a bluish white to milky whitedispersion can also be formed by a method of adding the above-describedorganic solution to water under stirring.

By separating and removing the organic solvent from the obtaineddispersion, the desired polyester water dispersion is obtained. Forexample, the desired polyester water dispersion is obtained by a methodof distilling off the hydrophilic organic solvent at atmosphericpressure or under reduced pressure. Incidentally, in the case where thepolyesters C and D are dissolved in a hydrophilic organic solventcapable of causing azeotropy with water, at the time of distilling offthe organic solvent, water causes azeotropy, and therefore, it isdesirable to disperse the polyester in a rather larger quantity of waterin advance while taking a weight loss of water into consideration.

In addition to the above, when the solid content concentration afterremoving the organic solvent exceeds 40% by weight, re-coagulation ofthe polyester to be dispersed in water is easily caused, and stabilityof the water dispersion is lowered. Therefore, it is preferable tocontrol the solid content concentration of the water dispersion to notmore than 40% by weight. On the other hand, when the concentration istoo small, a time required for drying becomes long, and therefore, alower limit of the solid content concentration is preferably 0.1% byweight or more. Even within the foregoing range, the solid contentconcentration of the aqueous coating solution which is used in thepresent invention is more preferably not more than 20% by weight, andespecially preferably 1 to 10% by weight relative to the weight of thecoating solution. When this proportion is less than 1% by weight, thereis a concern that the wettability with the polyester film isinsufficient. On the other hand, when this proportion exceeds 20% byweight, there is a concern that the stability of the coating solution orthe appearance of the coating layer is deteriorated.

Coating of the aqueous coating solution onto the laminated polyesterfilm can be carried out at an arbitrary stage. However, it is preferableto carryout coating in the production process of a laminated polyesterfilm, and it is more preferable to carry out coating on the film beforethe accomplishment of oriented crystallization.

The “film before the accomplishment of oriented crystallization” asreferred to herein includes an unstretched film, an uniaxially orientedfilm obtained by orienting an unstretched film in anyone of thelongitudinal direction and the lateral direction, a film obtained bystretching and orienting an unstretched film in two directions of thelongitudinal direction and the lateral direction at a low stretch ratio(biaxially stretched film before the accomplishment of orientedcrystallization by finally re-stretching the film in the longitudinaldirection or the lateral direction), and the like. Above all, it ispreferable that the above-described aqueous coating solution is coatedon an unstretched film or an uniaxially stretched film obtained byorienting an unstretched film in one direction and subjected tolongitudinal stretching and/or lateral stretching as well as heat set.

At the time of coating the aqueous coating solution on the film, as apreliminary treatment for the purpose of enhancing coating properties,the film surface may be subjected to a physical treatment such as acorona surface treatment, a flame treatment, a plasma treatment, etc.

The coating solution is used by adjusting its coating amount such thatthe thickness of the coating film falls within the foregoing range. As acoating method, a known arbitrary coating method can be applied. Forexample, a roll coating method, a gravure coating method, a roll brushmethod, a spray coating method, an air knife coating method, animpregnation method, a curtain coating method, and the like can beadopted solely or in combination. Above all, a roll coating method ispreferable, and among the roll coating methods, a gravure coating methodis more preferable.

[Production Method]

As for a method for producing the biaxially stretched laminatedpolyester film of the present invention, first of all, 51 layers or morein total of the polyester (A) for the first layer which is supplied froma first extruder and the polyester (B) for the second layer which issupplied from a second extruder are alternately superimposed in a moltenstate to obtain unstretched laminated sheet, which is then cast on arotating drum, thereby fabricating an unstretched laminated film.

Subsequently, the obtained unstretched laminated film is stretched intwo axial directions of the film forming direction (longitudinaldirection, longer direction, or MD direction) and the directionorthogonal thereto (lateral direction, width direction, or TDdirection). It is preferable to control a stretching temperature to arange of the glass transition temperature (Tg) to (Tg+50)° C. of thepolyester (A) and to control an area magnification of stretching to 5 to50 times.

In addition, in the case where not only the glass transition temperatureof the polyester (B) of the second layer is lower than 90° C., but aprotective layer having a thickness so as to contribute to the Young'smodulus properties is not provided, it is preferable to control the areamagnification of stretching to 17 times or more. When the stretch ratiois larger, the Young's modulus at 90° C. can be increased, theprocessability into a laminated glass increases, and simultaneously,scattering in the plane direction in each layer of the first layer andthe second layer becomes small due to thinning by stretching, whereby anoptical interference of the laminated film becomes uniform in the planedirection.

In addition, in the case where the glass transition temperature of thesecond layer is lower than 90° C., as for the stretch ratio for thepurpose of increasing the Young's modulus properties at 90° C., it ispreferable to carry out stretching in a ratio of 4.0 times or more inboth the film forming direction and the lateral direction.

The stretching method may be any method of sequential biaxial stretchingand simultaneous biaxial stretching.

Subsequently, this biaxially stretched laminated polyester film issubjected to a heat treatment. In the case where the biaxially stretchedlaminated polyester film is used for a planar laminated glass or thelike, it is preferable to carry out the heat treatment in a range of themelting point of the polyester of the second layer or higher to atemperature of 10° C. lower than the melting point of the polyester ofthe first layer. By carrying out the heat treatment within such atemperature range, the first layer is crystallized, the second layer ismelted to become non-oriented, and the difference in refractive indexbetween the layers as generated by stretching becomes larger, whereby ahigh reflectance can be obtained. When the heat treatment temperature isnot a temperature of 10° C. or more lower than the melting point of thepolyester of the first layer, there is a concern that the orientation ofthe molecular chain within the first layer is relieved, whereby therefractive index is lowered, and it becomes difficult to impart asufficient difference in refractive index to the obtained laminatedfilm.

In addition, in the case where the biaxially stretched laminatedpolyester film is used for a curved laminated glass or the like, it ispreferable that the film is provided with the above-described thermalshrinkage properties. For that reason, it is preferable to carry out theheat treatment in a temperature range of 150 to 210° C.

Application

The biaxially stretched laminated polyester film of the presentinvention has a high transmittance in a visible light wavelength regionand simultaneously has high reflection properties in a near-infraredwavelength region, and therefore, it can be widely used for applicationsin which it is required to shield heat rays. In particular, since thebiaxially stretched laminated polyester film of the present inventionhas excellent processability at the time of processing into a laminatedglass, it is suitably used for a laminated glass application and can beused for a laminated glass for a window such as a building window, anautomotive window, etc.

The laminated glass has a structure in which the biaxially stretchedlaminated polyester film of the present invention is sandwiched betweentwo glass sheets via a resin layer composed of at least one memberselected from an ethylene-vinyl acetate copolymer, polyvinyl butyral,and an ionomer resin. Examples of the processing method of a laminatedglass include a method of superimposing these lamination members andthen heating them while applying a pressure.

In the laminated glass of the present invention, it is preferable thatan ultraviolet light absorber is further contained in theabove-described resin layer in which polyvinyl butyral or the like isused.

On that occasion, a thickness of the resin layer is preferably 0.05 to20 μm, and more preferably 0.1 to 10 μm. In view of the fact that thethickness of the resin layer falls within this range, sufficientultraviolet light absorption properties can be obtained.

In addition, in the case where the resin layer contains an ultravioletlight absorber, it is preferable that an average light transmittance ofthe laminated glass within a wavelength range of 300 nm or more and lessthan 400 nm is not more than 10%.

At the time of being used as a laminated glass, in view of the fact thatthe above-described ultraviolet light absorber is further contained inthe resin layer, nevertheless the laminated polyester film including apolyethylene-2,6-naphthalenedicarboxylate layer having relatively lowultraviolet durability, even when it is used for heat ray shielding of awindow of a vehicle or a building, or the like for a long period oftime, cloudiness, yellowing, or the like of the film by an ultravioletlight can be efficiently suppressed, and high ultraviolet durability canbe imparted.

[Metal-Based Laminate]

In the present invention, the biaxially stretched laminated polyesterfilm of the present invention may be constituted such that a laminate ofa metal and/or a metal oxide having a laminated structure (II) in whicha low-refractive index layer and a high-refractive index layer arealternately laminated is further laminated on one surface thereof. Here,a difference in refractive index between the low-refractive index layerand the high-refractive index layer constituting the laminate of a metaland/or a metal oxide is preferably 0.1 or more, and more preferably 0.5or more. So long as the difference in refractive index between the bothlayers is satisfied with such a relation, the range of the refractiveindex of each layer is not particularly limited.

The metal can be used for the low-refractive index layer, and the metaloxide can be used for both the low-refractive index layer and thehigh-refractive index layer.

In addition, at the time of laminating the metal-based laminate on onesurface of the biaxially stretched laminated polyester film of thepresent invention, it is preferable that the biaxially stretchedlaminated polyester film has a protective layer of 5 μm or more and notmore than 20 μm. In the case where the thickness of the protective layeris less than the lower limit, there is a concern that when themetal-based laminate is laminated on one surface of the biaxiallystretched laminated polyester film of the present invention, the bothinterfere with each other to lower the visible light transmittance, andthe average reflectance in a visible light region as an infrared lightshielding structure composed of a combination thereof exceeds 30%.

On the other hand, in the case where the thickness of the protectivelayer exceeds the upper limit, there is a concern that when molded intoa curved laminated glass, the follow-up properties toward the curvedproportion tend to be lowered, and besides, a proportion of thethickness of the protective layer to the thickness of the laminatedstructure (I) of the biaxially stretched laminated polyester filmbecomes high, so that in the step of a molten state for fabricating thelaminated structure (I), the uniformity of the thickness of each otherof the laminated structure (I) is impaired, thereby causing scatteringin the reflectance properties.

(Metal)

Examples of the metal which is used for the laminate of a metal and/or ametal oxide used in the present invention include metals such as Au, Ag,Cu, Al, etc. Of these, Ag which does not substantially absorb a visiblelight is especially preferable. Incidentally, the metal forming themetal layer may be used in combination of two or more kinds thereof asthe need arises.

As a method of forming such a metal layer, a chemical vapor depositionmethod is preferable, and a vacuum vapor deposition method, a sputteringmethod, or a plasma CVD method is especially preferable. A thickness ofthe metal layer is in the range of 5 to 1,000 nm, and preferably 10 to500 nm. When the thickness of the metal layer is less than the lowerlimit, a sufficient heat ray shielding performance is hardly revealed.In addition, when the thickness of the metal layer exceeds the upperlimit, the visible light transmittance is easy to become insufficient,so that there is a concern that the transparency is impaired.

(Metal Oxide)

Examples of the metal oxide which is used in the present inventioninclude TiO₂, ZrO₂, SnO₂, In₂O₃, SiO₂, ITO, IZO, AZO, and the like.

Similar to the above-described method of forming a metal layer, a methodof forming such a metal oxide layer is preferably a chemical vapordeposition method, and especially preferably a vacuum vapor depositionmethod, a sputtering method, or a plasma CVD method. Though a thicknessof the metal oxide layer is related to a refractive index and athickness of other metal layer or metal oxide layer from the standpointof optical interference, it is preferably in the range of 0.1 to 750 nm,and more preferably in the range of 10 to 500 nm. When the thicknessfalls outside the foregoing range, there is a concern that an opticalinterference effect cannot be sufficiently obtained, and there is aconcern that the reflectance of a visible light increases, or a heat rayreflecting performance is lowered.

(Laminate)

Though the structure of the laminate of a metal and/or a metal oxide isnot particularly limited, for example, a structure in which a layer of ametal oxide is first formed as the high-refractive index layer, a metallayer is subsequently formed as the low-refractive index layer, and alayer composed of a metal oxide is finally formed as the high-refractiveindex layer, thereby sandwiching the metal layer by the metal oxidelayers is preferable because the reflectance in a visible light regioncan be decreased while keeping the high reflectance in an infraredregion due to a reflection preventing effect by the metal oxide. Inaddition, as another embodiment, a structure in which a metal oxidehaving a high refractive index and a metal oxide having a low refractiveindex are laminated, thereby reflecting an infrared light due tointerference is also preferable.

From the viewpoint of productivity, the layer number of the laminate ofa metal and/or a metal oxide is preferably not more than 40 layers, morepreferably not more than 30 layers, and still more preferably not morethan 10 layers. In addition, a lower limit of the layer number ispreferably 3 layers, and more preferably 5 layers.

[Infrared Light Shielding Structure]

It is preferable that the infrared light shielding structure in thepresent invention has a structure in which the above-described laminateof a metal and/or a metal oxide is laminated on one surface of theabove-described biaxially stretched laminated polyester film via theprotective layer of 5 μm or more and not more than 20 μm of thepolyester film.

In view of the fact that the infrared light shielding structure has sucha structure, the infrared light shielding structure is able to have botha high transmittance of a visible light and a high infrared lightshielding performance such that the average reflectance in a wavelengthrange of 400 to 750 nm is not more than 30%, the average reflectance ina wavelength range of 800 to 1,200 nm is 50% or more, and the averagereflectance in a wavelength range of 1,200 to 2,100 nm is 50% or more.In order to allow the average reflectance in a visible light region tofall within the foregoing range, by controlling the thickness of theprotective layer of the polyester-based laminated film on the side onwhich it is stuck to the metal-based laminate to a range of 5 μm or moreand not more than 20 μm, thereby making the thickness thicker than thatof the conventional one, the interference between these laminates iscancelled, and an infrared light shielding structure which is excellentin visible light transmission in addition to the heat ray shieldingperformance and suitable for a laminated glass is obtained.

The average reflectance of the infrared light shielding structure at 400to 750 nm is preferably not more than 25%. When the reflectance in thiswavelength region exceeds the upper limit, there is a concern that inthe case of being used for a laminated glass of an automotive windshieldrequiring high visibility, or the like, sufficient visibility is notobtained.

In addition, the average reflectance of the infrared light shieldingstructure in a wavelength range of 800 to 1,200 nm is preferably 60% ormore. When the reflectance in this wavelength region is less than thelower limit, for example, in the case of being stuck onto an automotivewindshield or the like and used, a sufficient near-infrared lightshielding effect is not obtained, and the temperature within theautomobile is easy to increase.

The average reflectance of the infrared light shielding structure in awavelength region of 1,200 to 2,100 nm is preferably 60% or more. Whenthe reflectance in this wavelength region is less than the lower limit,for example, in the case of being stuck onto an automobile windshield orthe like and used, a sufficient far-infrared light shielding effect isnot obtained, and a heat feeling felt by a human being within theautomobile becomes strong.

EXAMPLES

The present invention is hereunder described in more detail by referenceto the following Examples. Incidentally, physical properties andcharacteristics in the Examples were measured or evaluated by thefollowing methods.

(1) Layer Thickness:

A sample was cut into a triangle, fixed to an embedding capsule, andthen embedded with an epoxy resin. Then, the embedded sample was cutalong the film forming direction and the thickness direction by using amicrotome (ULTRACUTS, a manufacturer: Reichert), thereby producing athin film slice having a thickness of 50 nm. The obtained thin filmslice was observed and photographed at an accelerating voltage of 100 kVby using a transmission electron microscope (a manufacturer: JEOL Ltd.,a trade name: JEM2010), and a thickness of each layer was measured fromthe photographs.

Incidentally, in the case where distinguishing is difficult, the filmsample cut by the microtome may be dyed with 2% osmic acid at 60° C. for2 hours and measured for the thickness of the coating layer by using atransmission electron microscope (manufactured by JEOL Ltd., a tradename: JEM2010).

(2) Film Thickness:

A film thickness was measured at a stylus pressure of 30 g by using anelectron micrometer (a trade name: K-312A, manufactured by AnritsuCorporation).

(3) Average Reflectance:

A relative mirror reflectance to an aluminum vapor-deposited mirror wasmeasured over a wavelength range of 350 nm to 2,100 nm by using aspectral photometer (MPC-3100, manufactured by Shimadzu Corporation).Among the obtained spectra, an average reflectance obtained by averagingreflectances at 400 to 750 nm and an average reflectance obtainedaveraging reflectances at 800 to 1,200 nm were determined, respectively.

In addition, even in the case of measuring an average reflectance of theinfrared light shielding structure, a reflectance was measured accordingto the above-described method, and furthermore, an average reflectanceof reflectances in a wavelength range of 1,200 to 2,100 nm wasdetermined, too.

(4) Visible Light Transmittance and Solar Transmittance:

A relative spectral transmittance to a barium sulfate integrating sphereat each wavelength was measured in a wavelength range of 300 nm to 2,100nm by using a spectral photometer (MPC-3100, manufactured by ShimadzuCorporation). A visible light transmittance in a range of 400 to 750 nmand a solar transmittance in a wavelength region of 340 to 1,800 nm werecalculated from the obtained transmittance curve in conformity with JISR3106:1998.

(5) Glass Transition Temperature (Tg):

An internal loss tan δ of the obtained biaxially stretched film wasmeasured by using a dynamic viscoelasticity measuring device(manufactured by Orientec Co., Ltd., DDV-01FP) under a condition in ameasuring temperature range of 30 to 180° C. at a temperature rise rateof 2° C./min and at 1 Hz, and a glass transition temperature (Tg) of thefirst layer was determined from a peak temperature on the hightemperature side, and a glass transition temperature (Tg) of the secondlayer was determined from a peak temperature on the low temperatureside, respectively.

In addition, in the case where distinguishing of the glass transitiontemperature (Tg) of any layer is difficult by the above-describedmeasurement method, the glass transition temperature (Tg) of each layermay be determined by fabricating a single-layer biaxially stretched filmof a composition constituting each layer and measuring an internal losstan δ by using a dynamic viscoelasticity measuring device (manufacturedby Orientec Co., Ltd., DDV-01FP) according to the above-describedmeasurement condition.

(6) Young's Modulus:

A test piece obtained by cutting out the film into a size of 150 mm inlength and 10 mm in width is used and drawn in a chuck distance of 100mm at a tensile rate of 10 mm/rain and a chart rate of 500 mm/min in aroom regulated at a temperature of 20° C. and a humidity of 50% by usinga tensilon UCT-100, manufactured by Orientec Co., Ltd., and a Young'smodulus is calculated from a tangent of a rising part of an obtainedload-elongation curve. Incidentally, as for the Young's modulus in thelonger direction (longitudinal direction), a longitudinal direction (MDdirection) of the film is referred to as the measurement direction, andas for the Young's modulus in the width direction (lateral direction), alateral direction (TD direction) of the film is referred to as themeasurement direction. Each of the Young's moduli was measured 10 times,and an average value thereof was adopted.

In addition, the Young's modulus under a temperature atmosphere of 90°C. was determined by setting a test piece and a chuck portion of atensilon in a chamber set up to a temperature atmosphere of 90° C., andafter standing for 2 minutes, carrying out the above-described tensiletest.

(7) Polyester Component:

With respect to each layer of a film sample, each component andcopolymerization component amount of a polyester were determined bymeans of the ¹H-NMR measurement.

(8) Thermal Shrinkage Properties:

A film of 30 cm square in length, which has been measured for a preciselength in advance with respect to the longitudinal direction and thelateral direction of the film and marked, is put in an oven set up at120° C. under a no-load condition; after standing for 30 minutes, theresulting film is taken out and returned to room temperature; and adimensional change thereof is read.

A thermal shrinkage in each of the longitudinal direction and thelateral direction was determined from a length (L0) before the heattreatment and a dimensional change amount (ΔL) by the heat treatmentaccording to the following equation (2). The thermal shrinkage in eachof the directions was evaluated in a sample number of n=5, and anaverage value thereof was adopted.

Thermal shrinkage (%)=(ΔL/L0)×100  (2)

(9) Measurement of Melting Point and Crystallization Peak of Film byDSC:

With respect to 10 mg of a sample film, a temperature of acrystallization peak and a melting point of each layer were measured ata temperature rise rate of 20° C./min by using DSC (manufactured by TAInstruments, a trade name: DSC2920).

(10) Evaluation of Processability into a Laminated Glass: Evaluation ofProcessability into a Laminated Glass (i):

A film was sandwiched by two embossed sheets of polyvinyl butyral (PVB)having a thickness of 0.38 mm by using a laminator in such a manner thatthe embossed surface of each of the PVB sheets came into contact withthe film; the resultant was further sandwiched by two planar glasssheets having a thickness of 2 mm and a size of 500 mm×400 mm;thereafter, the assembly was put in a heating pressurizing furnace andtreated at 130° C. and 13 atm. for 30 minutes; only the temperature wasdecreased to 40° C. while maintaining the pressure; the pressure wasthen returned to ordinary pressure; the resultant was taken out from theheating pressurizing furnace; and the film protruded into thesurroundings of the glass sheets was cut off, thereby obtaining alaminated glass. As the polyvinyl butyral sheet, one with an embossedspace of approximately 1 mm was used.

The laminated glass obtained by the above-described method was visuallyobserved under a 30W fluorescent lamp light source. As a result, thecase where irregularities analogous to the embossed figures of PVB(irregularities having a diameter of not more than approximately 1 mm),wrinkles, glare, or air was observed in the sample glass is designatedas “X”, and the case where such was not observed is designated as “◯”.

In addition, with respect to the evaluation of processability into acurved laminated glass, a laminated glass was fabricated and evaluatedaccording to the above-described method, except that two curved glasssheets were used in place of the two planar glass sheets.

Evaluation of Processability into a Laminated Glass (ii):

The laminated glass obtained by the above-described method was visuallyobserved under a 30W fluorescent lamp light source. As a result, thecase where a reflected image into the sample glass was distorted isdesignated as “x”, and the case where a reflected image was notdistorted is designated as “◯”.

(11) Evaluation of Light Fastness:

An irradiation test was carried out by using a metal weather tester,manufactured by Daipla Wintes Co., Ltd. (a type: KW-R5TP-A, lightsource: water-cooled jacketed metal halide lamp) and a filter KF-1(transmitted light wavelength: 295 to 780 nm) at an irradiance of 75mW/cm² and a black panel temperature of 63° C. without spraying. A lighttransmittance of the film after the irradiation test was evaluated, anda light transmittance maintenance rate before and after the irradiation,which is expressed by the following equation (3), was evaluated.

Light transmittance maintenance rate=(Ta/Tb)×100  (3)

(In the foregoing equation, Ta represents a light transmittance afterthe irradiation; and Tb represents a light transmittance before theirradiation.)

(12) Haze Value:

A haze value of the film was measured using a haze meter, manufacturedby Nippon Denshoku Industries Co., Ltd. (NDH-2000) in conformity withJIS K7136.

(13) Refractive Index of Coating Layer:

A coating solution was dried and hardened in a plate state at 90° C. andmeasured with a laser light at a wavelength of 633 nm by using arefractive index meter (Prism Coupler, manufactured by MetriconCorporation).

Example 1

Polyethylene-2,6-naphthalate (hereinafter referred to as “PEN”) havingan intrinsic viscosity (in orthochlorophenol at 35° C.) of 0.62 dL/g asa polyester serving for not only a first layer but a protective layerand isophthalic acid-copolymerized polyethylene terephthalate having 12%by mole of isophthalic acid copolymerized therewith (hereinafterreferred to as “IA12PET”) and having an intrinsic viscosity (inorthochlorophenol at 35° C.) of 0.65 dL/g as a polyester serving for asecond layer were prepared, respectively.

Then, the polyester serving for not only the first layer but theprotective layer was dried at 180° C. for 5 hours, and the polyesterserving for the second layer was dried at 160° C. for 3 hours, andthereafter, the resulting polyesters were supplied into an extruder,respectively. PEN and IA12PET were heated to 300° C. and 280° C. andrendered in a molten state, respectively. The polyester serving for thefirst layer was branched into 90 layers, and the polyester serving forthe second layer was branched into 91 layers; thereafter, these branchedlayers were laminated by using a multilayer feed block apparatus forlaminating a laminated structure portion such that the polyester layerfor the first layer and the polyester layer for the second layer werealternately laminated, and a ratio of the maximum layer thickness to theminimum layer thickness in each of the first layer and the second layercontinuously changed up to 1.5 times in terms of maximum/minimum and theprotective layer on the both surfaces of the laminated structureportion; and the laminate was guided into a die while keeping alaminated state thereof and cast on a casting drum. Then, an unstretchedmultilayer laminated film having a protective layer composed of a PENlayer on the outermost layer on the both surfaces of the film and havinga total layer number of the laminated structure portion of 181 layerswas fabricated. Incidentally, with respect to the thickness of each ofthe laminated structure portion and the protective layer, the supplyamount was adjusted such that the thickness after stretching became asshown in Table 2.

This unstretched multilayer laminated film was stretched 4.0 times inthe film forming direction at a temperature of 150° C. and furtherstretched 4.0 times in the width direction at a temperature of 155° C.,followed by carrying out a heat set treatment at 230° C. for 3 seconds.Incidentally, the layer structure and the film forming condition areshown in Table 1, the layer structure of the resulting film is shown inTable 2, and the physical properties thereof are shown in Table 3.

Example 2

The same operation as that in Example 1 was repeated, except forchanging the stretch ratio to 4.5 times in the film forming directionand 4.5 times in the width direction, respectively as shown in Table 1and adjusting the thickness of each of the laminated structure portionand the protective layer as shown in Table 2. The layer structure of theresulting film is shown in Table 2, and the physical properties thereofare shown in Table 3.

Examples 3 and 4

The same operation as that in Example 1 was repeated, except foradjusting the thickness of the protective layer as shown in Table 2. Thelayer structure of each of the resulting films is shown in Table 2, andthe physical properties thereof are shown in Table 3.

Example 5

The same operation as that in Example 1 was repeated, except forchanging the stretch ratio to 3.5 times in the film forming directionand 3.5 times in the width direction, respectively as shown in Table 1and adjusting the thickness of each of the laminated structure portionand the protective layer as shown in Table 2. The layer structure of theresulting film is shown in Table 2, and the physical properties thereofare shown in Table 3.

Example 6

The same operation as that in Example 3 was repeated, except for using,as the polyester serving for the second layer, isophthalicacid-copolymerized polyethylene terephthalate having 20% by mole ofisophthalic acid copolymerized therewith (hereinafter referred to as“IA20PET”) and having an intrinsic viscosity (in orthochlorophenol at35° C.) of 0.65 dL/g. The layer structure of the resulting film is shownin Table 2, and the physical properties thereof are shown in Table 3.

Example 7

The same operation as that in Example 3 was repeated, except for using,as the polyester serving for the second layer, naphthalenedicarboxylicacid-copolymerized polyethylene terephthalate having 11% by mole of2,6-naphthalenedicarboxylic acid copolymerized therewith (hereinafterreferred to as “NDC11PET”) and having an intrinsic viscosity (inorthochlorophenol at 35° C.) of 0.65 dL/g. The layer structure of theresulting film is shown in Table 2, and the physical properties thereofare shown in Table 3.

Examples 8 and 9

The same operation as that in Example 1 was repeated, except forchanging the lamination number of each layer of the laminated structureportion and the thickness of the protective layer as shown in Tables 1and 2. The layer structure of each of the resulting films is shown inTable 2, and the physical properties thereof are shown in Table 3.

Example 10

The same operation as that in Example 2 was repeated, except forcarrying out the heat set treatment at a temperature of 170° C. Thelayer structure of the resulting film is shown in Table 2, and thephysical properties thereof are shown in Table 3.

In the present Example, the thermal shrinkage at 120° C. for 30 minuteswas 1.2% in the longitudinal direction and 1.2% in the lateraldirection, respectively; and similar to the evaluation of theprocessability into a planar laminated glass, in the evaluation of theprocessability into a laminated glass using a curved laminated glass,irregularities analogous to the embossed figures of PVB (irregularitieshaving a diameter of not more than approximately 1 mm), wrinkles, glare,and air were not observed, and favorable processability into a laminatedglass was obtained. In addition, by using the film of the presentExample for a curved laminated glass, more favorable processability intoa glass was obtained without causing distortion of an outline reflectedon the glass.

Example 11

On one surface of the biaxially stretched laminated film fabricated inExample 1, the following coating agent (I) was coated using a bar coaterand then dried, thereby forming an ultraviolet light absorber-containinglayer having a thickness of 6.3 μm.

A light irradiation test was carried out by using this laminated film.As a result, the sample of Example 1 had a light transmittancemaintenance rate of 80% according to the evaluation method (11).Meanwhile, the sample having an ultraviolet light absorber-containinglayer of the present Example had a light transmittance maintenance rateof 98% and was confirmed to have favorable durability against anultraviolet light.

(Preparation of Coating Agent (I))

8 parts by weight of TINUVIN (manufactured by Ciba) as an organicultraviolet light absorber, 60 parts by weight of HALSHYBRIDUV-G13(manufactured by Nippon Shokubai Co., Ltd.) that is an acrylic resin asa binder resin, and 0.6 parts by weight of DESMODUR N3200 (manufacturedby Sumika Bayer Urethane Co., Ltd.) as an isocyanate curing agent weredispersed in 31 parts by weight of toluene, thereby preparing a coatingagent (I) as a solution having a solid content concentration of 34% byweight and a concentration of the ultraviolet light absorber in thesolid content of 12% by weight.

Example 12

The same operation as that in Example 2 was repeated, except for using,as the polyester serving for the second layer, isophthalicacid-copolymerized polyethylene terephthalate (IA11PET) having anintrinsic viscosity of 0.90 dL/g, changing the stretch ratio to 4.0times in the film forming direction and 4.5 times in the widthdirection, respectively, and changing the heat set temperature to 170°C. Incidentally, the layer structure and the film forming condition areshown in Table 1, the layer structure of the resulting film is shown inTable 2, and the physical properties thereof are shown in Table 3.

In the present Example, the thermal shrinkage at 120° C. for 30 minuteswas 1.1% in the longitudinal direction and 1.2% in the lateraldirection, respectively; and similar to the evaluation of theprocessability into a planar laminated glass, in the evaluation of theprocessability into a laminated glass using a curved laminated glass,irregularities analogous to the embossed figures of PVB (irregularitieshaving a diameter of not more than approximately 1 mm), wrinkles, glare,and air were not observed, and favorable processability into a laminatedglass was obtained. In addition, by using the film of the presentExample for a curved laminated glass, more favorable processability intoa glass was obtained without causing distortion of an outline reflectedon the glass.

Example 13

The same operation as that in Example 12 was repeated, except forchanging the heat set temperature to 204° C. as shown in Table 1. Thelayer structure of the resulting film is shown in Table 2, and thephysical properties thereof are shown in Table 3.

In the present Example, the thermal shrinkage at 120° C. for 30 minuteswas 0.6% in the longitudinal direction and 0.7% in the lateraldirection, respectively; and similar to the evaluation of theprocessability into a planar laminated glass, in the evaluation of theprocessability into a laminated glass using a curved laminated glass,irregularities analogous to the embossed figures of PVB (irregularitieshaving a diameter of not more than approximately 1 mm), wrinkles, glare,and air were not observed, and favorable processability into a laminatedglass was obtained. In addition, by using the film of the presentExample for a curved laminated glass, more favorable processability intoa glass was obtained without causing distortion of an outline reflectedon the glass.

Example 14

The same operation as that in Example 12 was repeated, except for using,as the polyester serving for the second layer, isophthalicacid/naphthalenedicarboxylic acid-copolymerized polyethyleneterephthalate having 26% by mole of isophthalic acid and 9% by mole of2,6-naphthalenedicarboxylic acid copolymerized therewith (hereinafterreferred to as “IA26NDC9PET”) and having an intrinsic viscosity (inorthochlorophenol at 35° C.) of 0.70 dL/g, changing the stretch ratio to4.0 times in the width direction, and changing the heat set temperatureto 170° C. as shown in Table 1. The layer structure of the resultingfilm is shown in Table 2, and the physical properties thereof are shownin Table 3. Since IA26NDC9PET is amorphous, according to the results ofDSC measurement, a melting point on the low temperature side is notfound, but only a melting point of PEN of the first layer is measured.

In the present Example, the thermal shrinkage at 120° C. for 30 minuteswas 1.1% in the longitudinal direction and 1.2% in the lateraldirection, respectively; and similar to the evaluation of theprocessability into a planar laminated glass, in the evaluation of theprocessability into a laminated glass using a curved laminated glass,irregularities analogous to the embossed figures of PVB (irregularitieshaving a diameter of not more than approximately 1 mm), wrinkles, glare,and air were not observed, and favorable processability into a laminatedglass was obtained. In addition, by using the film of the presentExample for a curved laminated glass, more favorable processability intoa glass was obtained without causing distortion of an outline reflectedon the glass.

Comparative Example 1

The same operation as that in Example 1 was repeated, except foradjusting the thickness of the protective layer to 4 μm as shown inTable 2. The layer structure of the resulting film is shown in Table 2,and the physical properties thereof are shown in Table 3.

Comparative Example 2

The same operation as that in Example 9 was repeated, except for using,as the polyester serving for the second layer, a blend obtained by meltmixing terephthalic acid-copolymerized polyethylene-2,6-naphthalatehaving 8% by mole of terephthalic acid copolymerized therewith(hereinafter referred to as “TA8PEN”) and having an intrinsic viscosity(in orthochlorophenol at 35° C.) of 0.62 dL/g and NDC11PET in a weightratio of 8/2 (hereinafter referred to as “TA27PEN”) and adjusting thethickness of the protective layer to 5 μm as shown in Table 2. The layerstructure of the resulting film is shown in Table 2, and the physicalproperties thereof are shown in Table 3.

Comparative Example 3

The same operation as that in Example 3 was repeated, except for using,as the protective layer, the same IA12PET as that in the second layer,branching the polyester serving for the first layer into 91 layers, andbranching the polyester serving for the second layer into 90 layers. Thelayer structure of the resulting film is shown in Table 2, and thephysical properties thereof are shown in Table 3.

TABLE 1 Film production condition Laminated portion Protective layerportion First layer Second layer Stretch ratio Heat set Layer Tg LayerTg Layer Tg Total layer MD TD Temperature Resin number (° C.) Resinnumber (° C.) Resin number (° C.) number Times Times ° C. Example 1 PEN2 120 PEN 90 120 IA12PET 91 74 181 4.0 4.0 230 Example 2 PEN 2 120 PEN90 120 IA12PET 91 74 181 4.5 4.5 230 Example 3 PEN 2 120 PEN 90 120IA12PET 91 74 181 4.0 4.0 230 Example 4 PEN 2 120 PEN 90 120 IA12PET 9174 181 4.0 4.0 230 Example 5 PEN 2 120 PEN 90 120 IA12PET 91 74 181 3.53.5 230 Example 6 PEN 2 120 PEN 90 120 IA20PET 91 72 181 4.0 4.0 230Example 7 PEN 2 120 PEN 90 120 NDC11PET 91 80 181 4.0 4.0 230 Example 8PEN 2 120 PEN 138 120 IA12PET 139 74 277 4.0 4.0 230 Example 9 PEN 2 120PEN 45 120 IA12PET 46 74 91 4.0 4.0 230 Example 10 PEN 2 120 PEN 90 120IA12PET 91 74 181 4.5 4.5 170 Example 12 PEN 2 120 PEN 90 120 IA11PET 9174 181 4.0 4.5 170 (IV = 0.9) Example 13 PEN 2 120 PEN 90 120 IA11PET 9174 181 4.0 4.5 204 (IV = 0.9) Example 14 PEN 2 120 PEN 90 120IA26NDC9PET 91 75 181 4.0 4.0 170 (IV = 0.7) Comparative PEN 2 120 PEN90 120 IA12PET 91 74 181 4.0 4.0 230 Example 1 Comparative PEN 2 120 PEN45 120 TA27PEN 46 117 91 4.0 4.0 230 Example 2 Comparative IA12PET 2 74PEN 91 120 IA12PET 90 74 181 4.0 4.0 230 Example 3 PEN: Homo PENIA12PET: PET having 12% by mole of isophthalic acid copolymerizedtherewith IA20PET: PET having 20% by mole of isophthalic acidcopolymerized therewith NDC11PET: PET having 11% by mole of2,6-naphthalenedicarboxylic acid copolymerized therewith TA27PEN: Blendof TA8PEN and NDC11PET in a weight ratio of 8/2 IA26NDC9PET: PET having26% by mole of isophthalic acid and 9% by mole of2,6-naphthalenedicarboxylic acid copolymerized therewith

TABLE 2 Film layer structure Laminated structure portion Minimum MaximumProtective layer thickness thickness Whole Thickness Second Secondthickness Surface A Surface D First layer layer First layer layerThickness μm μm μm nm nm nm nm μm Example 1 36 5 5 114 127 171 190 26Example 2 46 10 10 114 127 171 190 26 Example 3 46 10 10 114 127 171 19026 Example 4 56 15 15 114 127 171 190 26 Example 5 46 10 10 114 127 171190 26 Example 6 46 10 10 114 127 171 190 26 Example 7 46 10 10 114 127171 190 26 Example 8 60 10 10 114 127 171 190 40 Example 9 33 10 10 114127 171 190 13 Example 10 46 10 10 114 127 171 190 26 Example 12 46 5 5114 127 171 190 26 Example 13 46 10 10 114 127 171 190 26 Example 14 4610 10 114 127 171 190 26 Comparative 34 4 4 114 127 171 190 26 Example 1Comparative 23 5 5 114 127 171 190 13 Example 2 Comparative 46 10 10 114127 171 190 26 Example 3

TABLE 3 Physical properties of film Results of DSC measurement Opticalproperties Melting Melting Average point on the point on the reflectancelow high 800 to 400 to Solar Visible light Crystallization temperaturetemperature 1,200 nm 750 nm transmittance transmittance Haze peak sideside % % % % % ° C. ° C. ° C. Example 1 77 17 67 85 — 130 224 262Example 2 77 17 67 85 — 130 224 262 Example 3 77 17 67 85 — 130 224 262Example 4 77 17 67 85 — 130 224 262 Example 5 69 17 70 86 — 130 224 262Example 6 81 18 63 85 — — — 262 Example 7 70 18 69 85 — 146 222 262Example 8 85 17 63 80 — 130 224 262 Example 9 60 18 74 83 — 130 224 262Example 10 61 15 74 92 1.5 — 224 262 Example 12 61 15 74 92 0.7 — 224262 Example 13 61 15 74 92 0.4 — 224 262 Example 14 65 17 72 87 0.3 — —262 Comparative 77 17 67 85 — 130 224 262 Example 1 Comparative 37 18 8082 — 126 213 262 Example 2 Comparative 77 10 67 90 — 130 224 262 Example3 Physical properties of film Measurement of dynamic viscoelasticity Tgon the Tg on the Evaluation of low high Young's modulus processabilitytemperature temperature (at 90° C.) into a laminated side side MD TDglass (i) ° C. ° C. GPa GPa (planar sheet) Example 1 78 149 2.5 2.5 ◯Example 2 78 149 3.0 3.0 ◯ Example 3 78 149 2.9 2.9 ◯ Example 4 78 1493.5 3.5 ◯ Example 5 78 149 2.8 2.9 ◯ Example 6 76 149 2.9 2.9 ◯ Example7 84 149 2.9 2.9 ◯ Example 8 78 149 2.9 2.9 ◯ Example 9 78 149 2.9 2.9 ◯Example 10 78 149 2.4 2.8 ◯ Example 12 78 149 2.2 2.6 ◯ Example 13 78149 2.3 2.7 ◯ Example 14 79 149 2.2 2.6 ◯ Comparative 78 149 2.3 2.3 XExample 1 Comparative 117 149 2.9 2.9 ◯ Example 2 Comparative 78 149 2.12.1 X Example 3

Example 15

Polyethylene-2,6-naphthalendicarboxylate (PEN) having an intrinsicviscosity (in orthochlorophenol at 35° C.) of 0.62 dL/g as a polyesterserving for a first layer and isophthalic acid-copolymerizedpolyethylene terephthalate having 12% by mole of isophthalic acidcopolymerized therewith (IA12PET) and having an intrinsic viscosity (inorthochlorophenol at 35° C.) of 0.65 dL/g as a polyester serving for asecond layer were prepared, respectively. Then, the polyester servingfor the first layer was dried at 180° C. for 5 hours, and the polyesterserving for the second layer was dried at 160° C. for 3 hours, andthereafter, the resulting polyesters were supplied into a separateextruder, respectively, and PEN and IA12PET were heated to 300° C. and280° C. and rendered in a molten state, respectively.

The polyester serving for the first layer was branched into 72 layers,and the polyester serving for the second layer was branched into 71layers; thereafter, these branched layers were laminated by using amultilayer feed block apparatus for alternately laminating the polyesterlayer for the first layer and the polyester layer for the second layer;and the laminate was guided into a die while keeping a laminated statethereof and cast on a casting drum. On that occasion, the thickness ofeach layer of the feed block was adjusted so as to have a thickness ofthe film and a thickness of each layer after stretching as shown inTable 5; the thickness of each layer in the alternately laminatedportion was adjusted such that it became gradually thick toward thethickness direction of the film; and each of the two layers to bedisposed as the outermost layer of the first layer was adjusted suchthat its thickness as the protective layer was 15% relative to the wholethickness. Thus, an unstretched laminated film having a total layernumber of the laminated portion of 141 layers excluding the protectivelayers was fabricated.

This unstretched laminated film was stretched 4.5 times in the filmforming direction (longitudinal direction) at a temperature of 150° C.and further stretched 4.5 times in the lateral direction at atemperature of 155° C., followed by carrying out a heat treatment at230° C. for 3 seconds. Incidentally, the layer structure and the filmforming condition are shown in Table 4, the structure of the resultingbiaxially stretched laminated film is shown in Table 5, and the physicalproperties thereof are shown in Table 6.

Example 16

PEN as a polyester serving for a first layer and a blend obtained byblending copolymerized polyethylene naphthalene dicarboxylate having 8%by mole of terephthalic acid copolymerized therewith (hereinafterreferred to as “TA8PEN” and having an intrinsic viscosity (inorthochlorophenol at 35° C.) of 0.63 dL/g and copolymerized polyethyleneterephthalate having 11% by moles of 2,6-naphthalenedicarboxylic acidcopolymerized therewith (hereinafter referred to as “NDC11PET”) andhaving an intrinsic viscosity (in orthochlorophenol at 35° C.) of 0.63dL/g in a weight ratio of 6/4 (hereinafter referred to as “TA44PEN”) asa polyester serving for a second layer were prepared, respectively.Then, the polyester serving for the first layer was dried at 180° C. for5 hours, and the polyester serving for the second layer was dried at160° C. for 3 hours, and thereafter, the resulting polyesters weresupplied into a separate extruder, respectively, and PEN and the mixedresin were heated to 300° C. and rendered in a molten state,respectively. The polyester serving for the first layer was branchedinto 72 layers, and the polyester serving for the second layer wasbranched into 71 layers; thereafter, these branched layers werelaminated by using a multilayer feed block apparatus for alternatelylaminating the polyester layer for the first layer and the polyesterlayer for the second layer; and the laminate was guided into a die whilekeeping a laminated state thereof and cast on a casting drum.

On that occasion, the thickness of each layer of the feed block wasadjusted so as to have a thickness of the film and a thickness of eachlayer after stretching as shown in Table 5; the thickness of each layerin the alternately laminated portion was adjusted such that it becamegradually thick toward the thickness direction of the film; and each ofthe two layers to be disposed as the outermost layer of the first layerwas adjusted such that its thickness as the protective layer was 15%relative to the whole thickness. Thus, an unstretched laminated filmhaving a total layer number of the laminated portion of 141 layersexcluding the protective layers was fabricated.

This unstretched laminated film was stretched 4.5 times in the filmforming direction (longitudinal direction) at a temperature of 150° C.and further stretched 4.5 times in the lateral direction at atemperature of 155° C., followed by carrying out a heat treatment at230° C. for 3 seconds. Incidentally, the layer structure and the filmforming condition are shown in Table 4, the structure of the resultingbiaxially stretched laminated film is shown in Table 5, and the physicalproperties thereof are shown in Table 6.

Example 17

The same operation as that in Example 16 was repeated, except forchanging the stretch ratio to 4.0 times in the film forming directionand 4.0 times in the lateral direction, respectively as shown in Table4. The structure of the resulting biaxially stretched laminated film isshown in Table 5, and the physical properties thereof are shown in Table6.

Example 18

The same operation as that in Example 16 was repeated, except for using,as the polyester serving for the second layer, a blend obtained byblending TA8PEN and NDC11PET in a weight ratio of 8/2 (hereinafterreferred to as “TA27PEN”) and changing the stretch ratio to 4.0 times inthe film forming direction and 4.0 times in the lateral direction,respectively as shown in Table 4. The structure of the resultingbiaxially stretched laminated film is shown in Table 5, and the physicalproperties thereof are shown in Table 6.

Example 19

The same operation as that in Example 15 was repeated, except for using138 layers for the first layer and 139 layers for the second layer ofthe laminated portion, thereby changing the total layer number of thealternately laminated portion to 277 layers as shown in Table 4 andadjusting the proportion of each of the protective layers composed ofthe polyester serving for the first layer to be formed on the bothsurfaces of the alternately laminated portion to 9% relative to thewhole thickness of the film. The structure of the resulting biaxiallystretched laminated film is shown in Table 5, and the physicalproperties thereof are shown in Table 6.

Example 20

The same operation as that in Example 15 was repeated, except for using415 layers for the first layer and 416 layers for the second layer ofthe laminated portion, thereby changing the total layer number of thealternately laminated portion to 831 layers as shown in Table 4 andadjusting the proportion of each of the protective layers composed ofthe polyester serving for the first layer to be formed on the bothsurfaces of the alternately laminated portion to 3% relative to thewhole thickness of the film. The structure of the resulting biaxiallystretched laminated film is shown in Table 5, and the physicalproperties thereof are shown in Table 6.

Example 21

The same operation as that in Example 16 was repeated, except for using138 layers for the first layer and 139 layers for the second layer ofthe laminated portion, thereby changing the total layer number of thealternately laminated portion to 277 layers as shown in Table 4 andadjusting the proportion of the protective layers composed of thepolyester serving for the first layer to be formed on the both surfacesof the alternately laminated portion to 9% relative to the wholethickness of the film. The structure of the resulting biaxiallystretched laminated film is shown in Table 5, and the physicalproperties thereof are shown in Table 6.

Example 22

The same operation as that in Example 16 was repeated, except for using415 layers for the first layer and 416 layers for the second layer ofthe laminated portion, thereby changing the total layer number of thealternately laminated portion to 831 layers as shown in Table 4 andadjusting the proportion of each of the protective layers composed ofthe polyester serving for the first layer to be formed on the bothsurfaces of the alternately laminated portion to 3% relative to thewhole thickness of the film. The structure of the resulting biaxiallystretched laminated film is shown in Table 5, and the physicalproperties thereof are shown in Table 6.

Example 23

The same operation as that in Example 21 was repeated, except forcarrying out the heat set treatment at a temperature of 170° C. as shownin Table 4. The structure of the resulting biaxially stretched laminatedfilm is shown in Table 5, and the physical properties thereof are shownin Table 6.

In the present Example, the thermal shrinkage at 120° C. for 30 minuteswas 1.2% in the longitudinal direction and 1.2% in the lateraldirection, respectively; and similar to the evaluation of theprocessability into a planar laminated glass, in the evaluation of theprocessability into a laminated glass using a curved laminated glass,irregularities analogous to the embossed figures of PVB (irregularitieshaving a diameter of not more than approximately 1 mm), wrinkles, glare,and air were not observed, and favorable processability into a laminatedglass was obtained. In addition, by using the film of the presentExample for a curved laminated glass, more favorable processability intoa glass was obtained without causing distortion of an outline reflectedon the glass.

Example 24

On one surface of the biaxially stretched laminated film fabricated inExample 15, the following coating agent (I) was coated using a barcoater and then dried, thereby forming an ultraviolet lightabsorber-containing layer having a thickness of 6.3 μm.

A light irradiation test was carried out by using this laminated film.As a result, the sample of Example 15 had a light transmittancemaintenance rate of 80% according to the evaluation method (11).Meanwhile, the sample having an ultraviolet light absorber-containinglayer of the present Example had a light transmittance maintenance rateof 98% and was confirmed to have favorable durability against anultraviolet light.

(Preparation of Coating Agent (I))

8 parts by weight of TINUVIN (manufactured by Ciba) as an organicultraviolet light absorber, 60 parts by weight of HALSHYBRID UV-G13(manufactured by Nippon Shokubai Co., Ltd.) that is an acrylic resin asa binder resin, and 0.6 parts by weight of DESMODUR N3200 (manufacturedby Sumika Bayer Urethane Co., Ltd.) as an isocyanate curing agent weredispersed in 31 parts by weight of toluene, thereby preparing a coatingagent (I) as a solution having a solid content concentration of 34% byweight and a concentration of the ultraviolet light absorber in thesolid content of 12% by weight.

Comparative Example 4

PEN as a polyester serving for a first layer and IA12PET as a polyesterserving for a second layer were prepared, respectively. Then, thepolyester serving for the first layer was dried at 180° C. for 3 hours,and the polyester serving for the second layer was dried at 160° C. for3 hours, and thereafter, the resulting polyesters were supplied into aseparate extruder, respectively, and PEN and IA12PET were heated to 300°C. and 280° C. and rendered in a molten state, respectively. Thepolyester serving for the first layer was branched into 140 layers, andthe polyester serving for the second layer was branched into 139 layers;thereafter, these branched layers were laminated by using a multilayerfeed block apparatus for alternately laminating the polyester layer forthe first layer and the polyester layer for the second layer; and thelaminate was guided into a die while keeping a laminated state thereofand cast on a casting drum.

On that occasion, the thickness of each layer of the feed block wasadjusted so as to have a thickness of the film and a thickness of eachlayer after stretching as shown in Table 5; the thickness of each layerin the alternately laminated portion was adjusted such that it becamegradually thick toward the thickness direction of the film; and each ofthe two layers to be disposed as the outermost layer of the first layerwas adjusted such that its thickness as the protective layer was 9%relative to the whole thickness. Thus, an unstretched laminated filmhaving a total layer number of the laminated structure portion of 277layers excluding the protective layers was fabricated.

This unstretched laminated film was stretched 3.5 times in the filmforming direction at a temperature of 150° C. and further stretched 4.0times in the lateral direction at a temperature of 155° C., followed bycarrying out a heat treatment at 230° C. for 3 seconds. Incidentally,the layer structure and the film forming condition are shown in Table 4,the layer structure of the resulting biaxially stretched laminated filmis shown in Table 5, and the physical properties thereof are shown inTable 6.

In the film of the present Comparative Example, the optical thicknessratio was out of 1.0, the ratio of the minim thickness and the maximumthickness was large, and a third-order reflection peak was generated ina visible region, and therefore, the reflectance in the visible lightwavelength region was high, and sufficient transparency was notobtained. In addition, the Young's modulus properties were notsufficient, and the processability into a laminated glass was lowered.

Comparative Example 5

The same operation as that in Example 15 was repeated, except forchanging the stretch ratio to 3.5 times in the film forming directionand 4.0 times in the lateral direction, respectively as shown in Table4. The structure of the resulting biaxially stretched laminated film isshown in Table 5, and the physical properties thereof are shown in Table6.

Comparative Example 6

The same operation as that in Example 15 was repeated, except for using15 layers for the first layer and 16 layers for the second layer of thelaminated portion, thereby changing the total layer number of thealternately laminated portion to 31 layers as shown in Table 4 andadjusting the proportion of each of the protective layers composed ofthe polyester serving for the first layer to be formed on the bothsurfaces of the alternately laminated portion to 32% relative to thewhole thickness of the film. The structure of the resulting biaxiallystretched laminated film is shown in Table 5, and the physicalproperties thereof are shown in Table 6.

Comparative Example 7

Polyethylene terephthalate (hereinafter referred to as “PET”) having anintrinsic viscosity (in orthochlorophenol at 35° C.) as a polyesterserving for a first layer and IA12PET as a polyester serving for asecond layer were prepared, respectively. Then, the polyester servingfor the first layer was dried at 170° C. for 3 hours, and the polyesterserving for the second layer was dried at 160° C. for 3 hours, andthereafter, the resulting polyesters were supplied into a separateextruder, respectively, and the polyesters were heated to 280° C. andrendered in a molten state, respectively. The polyester serving for thefirst layer was branched into 139 layers, and the polyester serving forthe second layer was branched into 138 layers; thereafter, thesebranched layers were laminated by using a multilayer feed blockapparatus for alternately laminating the polyester layer for the firstlayer and the polyester layer for the second layer; and the laminate wasguided into a die while keeping a laminated state thereof and cast on acasting drum.

On that occasion, the thickness of each layer of the feed block wasadjusted so as to have a thickness of the film and a thickness of eachlayer after stretching as shown in Table 5, and such that the thicknessof each layer in the alternately laminated portion became graduallythick toward the thickness direction of the film. Thus, an unstretchedlaminated film having a total layer number of the laminated structureportion of 277 layers was fabricated.

This unstretched laminated film was stretched 4.0 times in the filmforming direction at a temperature of 90° C. and further stretched 4.0times in the lateral direction at a temperature of 95° C., followed bycarrying out a heat treatment at 230° C. for 3 seconds. Incidentally,the layer structure and the film forming condition are shown in Table 4,the structure of the resulting biaxially stretched laminated film isshown in Table 5, and the physical properties thereof are shown in Table6.

Comparative Example 8

PET as a polyester serving for a first layer and TA44PEN as a polyesterserving for a second layer were prepared, respectively. Then, thepolyester serving for the first layer was dried at 170° C. for 3 hours,and the polyester serving for the second layer was dried at 160° C. for3 hours, and thereafter, the resulting polyesters were supplied into aseparate extruder, respectively, and PET and TA44PEN were heated to 280°C. and 300° C. and rendered in a molten state, respectively. Thepolyester serving for the first layer was branched into 72 layers, andthe polyester serving for the second layer was branched into 71 layers;thereafter, these branched layers were laminated by using a multilayerfeed block apparatus for alternately laminating the polyester layer forthe first layer and the polyester layer for the second layer; and thelaminate was guided into a die while keeping a laminated state thereofand cast on a casting drum.

On that occasion, the thickness of each layer of the feed block wasadjusted so as to have a thickness of the film and a thickness of eachlayer after stretching as shown in Table 5; the thickness of each layerin the alternately laminated portion was adjusted such that it becamegradually thick toward the thickness direction of the film; and each ofthe two layers to be disposed as the outermost layer of the first layerwas adjusted such that its thickness as the protective layer was 15%relative to the whole thickness. Thus, an unstretched laminated filmhaving a total layer number of the laminated structure portion of 141layers excluding the protective layers was fabricated.

This unstretched laminated film was stretched 4.0 times in the filmforming direction at a temperature of 100° C. and further stretched 4.0times in the lateral direction at a temperature of 105° C., followed bycarrying out a heat treatment at 230° C. for 3 seconds. Incidentally,the layer structure and the film forming condition are shown in Table 4,the layer structure of the resulting biaxially stretched laminated filmis shown in Table 5, and the physical properties thereof are shown inTable 6.

TABLE 4 Protective layer portion Proportion to the Laminated portionwhole thickness (%) First layer Second layer Stretch ratio Heat setSurface A Surface D Layer Layer Total layer MD TD Temperature Resin sideside Whole Resin number Resin number number Times Times ° C. Example 15PEN 11 11 21 PEN 70 IA12PET 71 141 4.5 4.5 230 Example 16 PEN 11 11 21PEN 70 TA44PEN 71 141 4.5 4.5 220 Example 17 PEN 11 11 21 PEN 70 TA44PEN71 141 4.0 4.0 220 Example 18 PEN 11 11 21 PEN 70 TA27PEN 71 141 4.0 4.0230 Example 19 PEN 6 6 12 PEN 139 IA12PET 138 277 4.5 4.5 230 Example 20PEN 2 2 4 PEN 416 IA12PET 415 831 4.5 4.5 230 Example 21 PEN 6 6 12 PEN139 TA44PEN 138 277 4.5 4.5 230 Example 22 PEN 2 2 4 PEN 416 TA44PEN 415831 4.5 4.5 230 Example 23 PEN 6 6 12 PEN 139 TA44PEN 138 277 4.5 4.5170 Comparative PEN 8 8 16 PEN 139 IA12PET 138 277 3.5 4.0 230 Example 4Comparative PEN 11 11 21 PEN 70 IA12PET 71 141 3.5 4.0 230 Example 5Comparative PEN 27 27 55 PEN 15 IA12PET 16 31 4.5 4.5 230 Example 6Comparative PET 0 0 0 PET 139 IA12PET 138 277 4.0 4.0 230 Example 7Comparative PET 11 11 21 PET 70 TA44PEN 71 141 4.0 4.0 230 Example 8

TABLE 5 Whole Protective layer Minimum layer Maximum thickness thicknessSurface A Surface D First layer Second layer First layer Second layer μmμm μm nm nm nm nm Example 15 28 3 3 123 138 170 192 Example 16 28 3 3122 132 194 210 Example 17 28 3 3 122 132 194 210 Example 18 28 3 3 122132 194 210 Example 19 49 3 3 123 138 170 192 Example 20 135 3 3 123 138170 192 Example 21 49 3 3 118 123 165 171 Example 22 135 3 3 118 123 165171 Example 23 49 3 3 118 123 165 171 Comparative 51 4 4 93 101 203 171Example 4 Comparative 28 3 3 123 138 170 192 Example 5 Comparative 11 33 123 138 170 192 Example 6 Comparative 43 0 0 123 138 170 192 Example 7Comparative 28 3 3 120 120 168 168 Example 8

TABLE 6 Measurement of dynamic Young's Optical propertiesviscoelasticity modulus Average reflectance Solar Visible light Tg onthe low Tg on the high (at 20° C.) 800 to 1,200 nm 400 to 750 nmtransmittance transmittance temperature side temperature side MD TD % %% % ° C. ° C. GPa GPa Example 15 79 13 68 89 78 149 5.2 5.2 Example 1654 15 72 86 107 149 4.8 4.9 Example 17 54 15 72 86 107 149 4.7 4.9Example 18 54 15 72 86 117 149 4.7 4.9 Example 19 90 14 64 87 78 149 5.25.2 Example 20 93 13 61 88 78 149 5.2 5.2 Example 21 62 14 74 85 107 1494.8 4.9 Example 22 86 12 65 84 107 149 4.8 4.9 Example 23 50 14 75 83107 149 4.8 4.9 Comparative 76 50 41 52 78 149 4.5 4.6 Example 4Comparative 68 20 68 83 78 149 4.9 4.9 Example 5 Comparative 41 13 81 8978 149 5.2 5.2 Example 6 Comparative 71 11 72 92 78 116 4.3 5.0 Example7 Comparative 23 12 86 87 107 116 4.3 5.0 Example 8 Thermal shrinkageYoung's (at 120° C. DSC properties Evaluation of modulus for 30 Meltingpoint on Melting point on processability (at 90° C.) minutes)Crystallization the low the high into a laminated MD TD MD TD peaktemperature side temperature side glass (i) GPa GPa % % ° C. ° C. ° C.(planar sheet) Example 15 2.4 2.4 0.6 0.6 126 225 260 ◯ Example 16 2.92.9 0.7 0.6 173 208 257 ◯ Example 17 2.8 2.8 0.4 0.4 173 208 257 ◯Example 18 2.9 2.9 0.4 0.4 153 213 258 ◯ Example 19 2.4 2.4 0.4 0.4 126225 260 ◯ Example 20 2.4 2.4 0.4 0.4 126 225 260 ◯ Example 21 2.9 2.90.4 0.4 173 208 257 ◯ Example 22 2.9 2.9 0.4 0.4 173 208 257 ◯ Example23 2.9 2.9 1.2 1.2 — 208 257 ◯ Comparative 1.7 1.5 0.5 0.2 126 225 260 XExample 4 Comparative 2.3 2.3 0.4 0.5 126 225 260 X Example 5Comparative 2.4 2.4 0.4 0.4 126 225 260 ◯ Example 6 Comparative 1.6 1.90.8 0.8 121 225 251 X Example 7 Comparative 1.6 1.9 0.8 0.8 173 208 251X Example 8

Example 25

Polyethylene-2,6-naphthalate (PEN) having an intrinsic viscosity (inorthochlorophenol at 35° C.) of 0.62 dL/g as a polyester serving for notonly a first layer but a protective layer and isophthalicacid-copolymerized polyethylene terephthalate having 12% by mole ofisophthalic acid copolymerized therewith (IA12PET) and having anintrinsic viscosity (in orthochlorophenol at 35° C.) of 0.65 dL/g as apolyester serving for a second layer were prepared, respectively.

Then, the polyester serving for not only the first layer but theprotective layer was dried at 180° C. for 5 hours, and the polyesterserving for the second layer was dried at 160° C. for 3 hours, andthereafter, the resulting polyesters were supplied into an extruder,respectively. PEN and IA12PET were heated to 300° C. and 280° C. andrendered in a molten state, respectively. The polyester serving for thefirst layer was branched into 90 layers, and the polyester serving forthe second layer was branched into 91 layers; thereafter, these branchedlayers were laminated by using a multilayer feed block apparatus forlaminating a laminated structure portion such that the polyester layerfor the first layer and the polyester layer for the second layer werealternately laminated, and a ratio of the maximum layer thickness to theminimum layer thickness in each of the first layer and the second layercontinuously changed up to 1.5 times in terms of maximum/minimum and theprotective layer on the both surfaces of the laminated structureportion; and the laminate was guided into a die while keeping alaminated state thereof and cast on a casting drum. Then, an unstretchedmultilayer laminated film having a protective layer composed of a PENlayer on the outermost layer on the both surfaces of the film and havinga total layer number of the laminated structure portion of 181 layerswas fabricated. Incidentally, with respect to the thickness of each ofthe laminated structure portion and the protective layer, the supplyamount was adjusted such that the thickness after stretching became asshown in Table 7.

This unstretched multilayer laminated film was stretched 4.5 times inthe film forming direction at a temperature of 150° C., and an aqueouscoating solution of a coating agent shown in Table 8 having aconcentration of 6% was uniformly coated on the both surfaces thereof byusing a roll coater. Subsequently, the resultant was supplied into atenter, stretched 4.5 times in the width direction at a temperature of155° C., and subsequently subjected to a heat set treatment at 204° C.for 3 seconds. The properties of the resulting film are shown in Table8.

<Coating Agent Component> (Polyester C)

A polyester C is constituted of, as an acid component, 90% by mole of2,6-naphthalenedicarboxylic acid/6% by mole of isophthalic acid/4% bymole of 5-sodium sulfoisophthalic acid and, as a diol component, 25% bymole of ethylene glycol/60% by mole of9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene/15% by mole of diethyleneglycol (Tg=115° C.).

Such a polyester C was produced in the following manner. That is, 100parts of dimethyl 2,6-naphthalenedicarboxylate, 5.3 parts of dimethylisophthalate, 5.4 parts of dimethyl 5-sodium sulfoisophthalate, 45 partsof ethylene glycol, and 78.3 parts of9,9-bis(4-(-hydroxyethoxy)phenyl)fluorene were charged into an esterinterchange reactor, to which was then added 0.1 parts of tetrabutoxytitanium, the contents were heated under a nitrogen atmosphere bycontrolling the temperature at 230° C., and formed methanol wasdistilled off, thereby achieving an ester interchange reaction.

Subsequently, 0.5 parts of IRGANOX 1010 (manufactured by Ciba-Geigy) wasadded to this reaction system; the temperature was gradually increasedto 255° C.; the inside of the system was evacuated to 1 mmHg to carryout a polycondensation reaction while removing an excess of the ethyleneglycol, thereby obtaining a copolymerized polyester C having anintrinsic viscosity of 0.48 dL/g.

20 parts of this copolymerized polyester C was dissolved in 80 parts oftetrahydrofuran, and 180 parts of water was dropped in the resultingsolution under a high-speed stirring of 10,000 rpm, thereby obtaining abluish milky white dispersion. Subsequently, this dispersion wasdistilled under a reduced pressure of 20 mmHg, thereby distilling offthe tetrahydrofuran. There was thus obtained a polyester waterdispersion having a solid content concentration of 10 wt %.

(Polyester D)

A polyester D is constituted of, as an acid component, 97% by mole ofterephthalic acid/1% by mole of isophthalic acid/2% by mole of 5-sodiumsulfoisophthalic acid and, as a diol component, 60% by mole of ethyleneglycol/40% by mole of bisphenol A (Tg=70° C.).

Such a polyester D was produced in the following manner. That is, 100parts of dimethyl terephthalate, 3 parts of dimethyl isophthalate, 1part of dimethyl 5-sodium sulfoisophthalate, 26 parts of ethyleneglycol, and 14 parts of a bisphenol A-propylene oxide adduct werecharged into an ester interchange reactor, to which was then added 0.1parts of tetrabutoxy titanium, the contents were heated under a nitrogenatmosphere by controlling the temperature at 230° C., and formedmethanol was distilled off, thereby achieving an ester interchangereaction.

Subsequently, 0.5 parts of IRGANOX 1010 (manufactured by Ciba-Geigy) wasadded to this reaction system; the temperature was gradually increasedto 255° C.; the inside of the system was evacuated to 1 mmHg to carryout a polycondensation reaction, thereby obtaining a copolymerizedpolyester D having an intrinsic viscosity of 0.48 dL/g.

20 parts of this copolymerized polyester D was dissolved in 80 parts oftetrahydrofuran, and 180 parts of water was dropped in the resultingsolution under a high-speed stirring of 10,000 rpm, thereby obtaining abluish milky white dispersion. Subsequently, this dispersion wasdistilled under a reduced pressure of 20 mmHg, thereby distilling offthe tetrahydrofuran. There was thus obtained a polyester waterdispersion having a solid content concentration of 10 wt %.

(Acrylic Resin)

An acrylic resin is constituted of 30% by mole of methylmethacrylate/30% by mole of 2-isopropenyl-2-oxazoline/10% by mole ofpolyethylene oxide (n=10) methacrylate/30% by mole of acrylamide (Tg=50°C., molecular weight: 350,000, refractive index: 1.50, density: 1.2g/cm³).

Such an acrylic resin was produced in the following manner. That is, afour-necked flask was charged with 302 parts of ion-exchanged water; thetemperature was increased to 60° C. in a nitrogen gas stream;subsequently, 0.5 parts of ammonium persulfate and 0.2 parts of sodiumbisulfite were added as polymerization initiators; and furthermore, amixture of 23.3 parts of methyl methacrylate, 22.6 parts of2-isopropenyl-2-oxazoline, 40.7 parts of polyethylene oxide (n=10)methacrylate, and 13.3 parts of acrylamide as monomers was dropped over3 hours while adjusting a liquid temperature to 60 to 70° C. Even aftercompletion of dropping, the reaction was continued with stirring whilekeeping the same temperature range for 2 hours, and subsequently, theresultant was cooled to obtain an acrylic water dispersion having asolid content of 25%.

(Organic Particle 1)

Acrylic filler (average particle diameter: 100 nm, refractive index:1.50, density: 1.2 g/cm³) (MX-100W, manufactured by Nippon Shokubai Co.,Ltd.)

(Surfactant)

Polyoxyethylene (n=7) lauryl ether (manufactured by Sanyo ChemicalIndustries, Ltd., a trade name: NAROACTY, N-70)

Examples 26 and 30

Laminated films were obtained in the same manner as that in Example 25,except for changing the proportions of the polyesters C and Dconstituting the coating layer as shown in Table 8. The obtainedproperties are shown in Table 8.

Examples 27, 28, 31 and 32

Laminated films were obtained in the same manner as that in Example 26,except for changing the thickness of the coating layer as shown in Table8. The obtained properties are shown in Table 8.

Example 29

A laminated film was obtained in the same manner as that in Example 26,except for changing the structure and production condition of thepolyester film onto which the coating layer was applied to those in Film2 as shown in Table 7. The obtained properties are shown in Table 8.

TABLE 7 Film 1 Film 2 Film Protective layer portion Resin PEN PENproduction Layer number 2 2 condition Tg (° C.) 120 120 Laminated layerFirst layer Resin PEN PEN portion Layer number 90 70 Second layer ResinIA12PET TA44PEN Layer number 91 71 Total layer number 181 141 Stretchratio MD Times 4.5 4.5 TD Times 4.5 4.5 Heat set Temperature ° C. 204220 Film layer Total thickness μm 46 28 structure Protective ThicknessSurface A μm 10 3 layer Surface D μm 10 3 Laminated Minimum First layernm 114 114 structure thickness Second layer nm 127 127 portion MaximumFirst layer nm 171 171 thickness Second layer nm 190 190 Thickness μm 2622

TABLE 8 Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple ple ple ple pleple ple Example Item 25 26 27 28 29 30 31 32 Coating layer CoatingComposition ratio Polyester C 21.2 42.25 42.25 42.25 42.25 59.2 42.2542.25 agent (% by weight) Polyester D 63.3 42.25 42.25 42.25 42.25 25.342.25 42.25 Acrylic resin 5 5 5 5 5 5 5 5 Organic particle 0.5 0.5 0.50.5 0.5 0.5 0.5 0.5 Surfactant 10 10 10 10 10 10 10 10 Ratio ofpolyester (% Polyester C 25.1 50 50 50 50 70 50 50 by weight) PolyesterD 74.9 50 50 50 50 30 50 50 Biaxially Type of laminated film Film 1 Film1 Film 1 Film 1 Film 2 Film 1 Film 1 Film 1 stretched Refractive indexof coating 1.63 1.61 1.61 1.61 1.61 1.59 1.61 1.61 multilayer layerlaminated Thickness of coating μm 0.08 0.08 0.05 0.20 0.08 0.08 0.030.25 film layer Haze value % 1.70 1.70 1.40 3.10 1.20 1.70 1.10 3.60Average reflectance at % 16 16 16 16 15 16 16 16 400 to 750 nm Averagereflectance at % 55 55 55 55 54 55 55 55 800 to 1,200 nm Young's modulus(at 90° C.), MPa 2.9 2.9 2.9 2.9 2.4 2.9 2.9 2.9 MD Young's modulus (at90° C.), MPa 2.9 2.9 2.9 2.9 2.4 2.9 2.9 2.9 TD Laminated Appearance(planar sheet) Evaluation of ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ glass processability into alaminated glass (i) Evaluation of ◯ ◯ ◯ ◯ ◯ X X X processability into alaminated glass (ii)

Example 33

Polyethylene-2,6-naphthalate (PEN) having an intrinsic viscosity (inorthochlorophenol at 35° C.) of 0.62 dL/g as a polyester serving for notonly a first layer but an outermost layer (protective layer) andisophthalic acid-copolymerized polyethylene terephthalate having 12% bymole of isophthalic acid copolymerized therewith (IA12PET) and having anintrinsic viscosity (in orthochlorophenol at 35° C.) of 0.65 dL/g as apolyester serving for a second layer were prepared, respectively.

Then, the polyester serving for not only the first layer but theprotective layer was dried at 180° C. for 5 hours, and the polyesterserving for the second layer was dried at 160° C. for 3 hours, andthereafter, the resulting polyesters were supplied into an extruder,respectively. PEN and IA12PET were heated to 300° C. and 280° C. andrendered in a molten state, respectively. The polyester serving for thefirst layer was branched into 90 layers, and the polyester serving forthe second layer was branched into 91 layers; thereafter, these branchedlayers were laminated by using a multilayer feed block apparatus forlaminating a laminated structure portion such that the polyester layerfor the first layer and the polyester layer for the second layer werealternately laminated, and a ratio of the maximum layer thickness to theminimum layer thickness in each of the first layer and the second layercontinuously changed up to 1.5 times in terms of maximum/minimum and theprotective layer on the both surfaces of the laminated structureportion; and the laminate was guided into a die while keeping alaminated state thereof and cast on a casting drum. Then, an unstretchedmultilayer laminated film having a protective layer composed of a PENlayer on the outermost layer on the both surfaces of the film and atotal layer number of the laminated structure portion of 181 layers wasfabricated. Incidentally, with respect to the thickness of each of thelaminated structure portion and the protective layer, the supply amountwas adjusted such that the thickness after stretching became as shown inTable 9.

This unstretched multilayer laminated film was stretched 4.5 times inthe film forming direction at a temperature of 150° C. Subsequently, theresultant was supplied into a tenter, stretched 4.5 times in the widthdirection at a temperature of 155° C., and subsequently subjected to aheat set treatment at 235° C. for 3 seconds. The properties of theresulting biaxially stretched laminated polyester film (Film 3) areshown in Tables 9 and 11.

On one surface of the resulting biaxially stretched laminated polyesterfilm, titanium oxide (TiO₂, refractive index 2.2) and silicon dioxide(SiO₂, refractive index: 1.5) were formed in a constitution of Laminate1 shown in Table 10 by a sputtering method. The properties of theresulting infrared light shielding structure are shown in Table 11.

In the infrared light shielding structure of the present Example, theinterference between the laminates in a visible light wavelength rangeat 400 to 750 nm was cancelled, and as a result, the average reflectancein the foregoing wavelength range was extremely low as 22%, and a highvisible light transmittance was obtained. Furthermore, nevertheless hightransmittance properties in a visible light region were reveaed, highreflectance properties in an infrared wavelength region were provided,and the solar transmittance became high in proportion to an increase ofthe transmittance to a visible light as compared with Example 36 inwhich the thickness of the protective layer is thin.

In addition, in the case of using the resulting film for a laminatedglass of a windshield, high visibility and high heat ray shieldingproperties were obtained.

Example 34

The same operation as that in Example 33 was repeated, except thatsilver (Ag, refractive index: 0.17) and indium oxide (In₂O₃, refractiveindex: 1.9) were formed in a constitution of Laminate 2 shown in Table10 as the metal/metal oxide laminate by a sputtering method in place ofTiO₂ and SiO₂. The properties of the resulting infrared light shieldingstructure are shown in Table 11.

Example 35

The same operation as that in Example 33 was repeated, except thatsilver (Ag) and indium oxide (In₂O₃) were formed in a constitution ofLaminate 3 shown in Table 10 as the metal/metal oxide laminate by asputtering method in place of TiO₂ and SiO₂. The properties of theresulting infrared light shielding structure are shown in Table 11.

Examples 36 to 38

The same operation as that in Example 33 was repeated, except that Film4 prepared by repeating the same operation as that in Example 33, exceptfor changing the thickness of the protective layer of the biaxiallystretched laminated polyester film to 3 μm, was used as the biaxiallystretched laminated polyester film, and the type of the metal/metaloxide laminate was changed as shown in Table 11. The properties of eachof the resulting infrared light shielding structures are shown in Table11.

Example 39

The same operation as that in Example 33 was repeated, except for notforming the metal/metal oxide laminate. The properties of the resultinginfrared light shielding structure are shown in Table 11.

Comparative Example 9

A polyethylene terephthalate film having a thickness of 50 μm was usedin place of the biaxially stretched laminated polyester film, and themetal/metal oxide having the structure of Laminate 1 shown in Table 10was formed on one surface thereof in the same method as that in Example33. The properties of the resulting infrared light shielding structureare shown in Table 11.

TABLE 9 Film 3 Film 4 Film Outermost layer portion Resin PEN PENproduction Layer number 2 2 condition Glass transition temperature 120120 (Tg) (° C.) Laminated structure portion First layer Resin PEN PENLayer number 90 90 Second layer Resin IA12PET IA12PET Layer number 91 91Total layer number 181 181 Stretch ratio MD Times 4.5 4.5 TD Times 4.54.5 Heat set Temperature ° C. 235 235 Film layer Total thickness μm 4632 structure Outermost Thickness Surface on μm 10 3 layer the metallayer side Opposite μm 10 3 surface to the metal layer side LaminatedMinimum First layer nm 114 114 structure thickness Second layer nm 127127 portion Maximum First layer nm 171 171 thickness Second layer nm 190190 Thickness μm 26 26 Film DSC Tg of second layer polymer ° C. 78 78properties measurement Tg of first layer polymer ° C. 120 120 Dynamic Tgof second layer polymer ° C. 78 78 viscoelasticity Tg of first layerpolymer ° C. 149 149

TABLE 10 Order Laminate 1 Laminate 2 Laminate 3 of Material ThicknessMaterial Thickness Material Thickness layer quality (nm) quality (nm)quality (nm) 1 TiO₂ 152 In₂O₃ 1.5 In₂O₃ 35 2 SiO₂ 33 Ag 12 Ag 10 3 TiO₂22 In₂O₃ 1.5 In₂O₃ 70 4 SiO₂ 233 (Film side) Ag 11 5 TiO₂ 22 In₂O₃ 70 6SiO₂ 33 Ag 10 7 TiO₂ 142 In₂O₃ 35 8 SiO₂ 31 (Film side) 9 TiO₂ 20 10SiO₂ 218 11 TiO₂ 20 12 SiO₂ 31 13 TiO₂ 132 14 SiO₂ 29 15 TiO₂ 19 16 SiO₂202 17 TiO₂ 19 18 SiO₂ 29 19 TiO₂ 122 20 SiO₂ 27 21 TiO₂ 17 22 SiO₂ 18723 TiO₂ 17 24 SiO₂ 27 25 TiO₂ 112 26 SiO₂ 24 27 TiO₂ 16 28 SiO₂ 171 29TiO₂ 16 30 SiO₂ 24 (Film side)

TABLE 11 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Com- ple ple ple pleple ple ple parative Item 33 34 35 36 37 38 39 Example 9 InfraredBiaxially stretched laminated Film 3 Film 3 Film 3 Film 4 Film 4 Film 4Film 3 PET light polyester film shielding Metal/metal oxide laminateLami- Lami- Lami- Lami- Lami- Lami- No Laminate 1 structure nate 1 nate2 nate 3 nate 1 nate 2 nate 3 Biaxially Average reflectance (%)    400to 750 nm 17 17 17 17 17 17 17 13 stretched   800 to 1,200 nm 77 77 7777 77 77 77 13 laminated Young's modulus (at 90° C.), MD MPa 3.0 3.0 3.02.4 2.4 2.4 3.0 3.3 polyester Young's modulus (at 90° C.), TD MPa 3.03.0 3.0 2.4 2.4 2.4 3.0 3.5 film Evaluation of processability into a ◯ ◯◯ ◯ ◯ ◯ ◯ ◯ laminated glass (i) (planar sheet) Properties Averagereflectance (%)    400 to 750 nm 22 24 20 35 39 31 17 22 of infrared  800 to 1,200 nm 77 84 87 77 84 87 77 28 light 1,200 to 2,100 nm 75 8287 75 82 87 14 69 shielding Solar transmittance (%) 52 48 49 46 40 43 6369 structure

INDUSTRIAL APPLICABILITY

Since the biaxially stretched laminated polyester film of the presentinvention has both a high near-infrared shielding performance andexcellent processability into a laminated glass, it is possible toprovide a laminated glass having excellent appearance and highnear-infrared shielding performance.

1. A biaxially stretched laminated polyester film comprising 51 layersor more in total, in which a first layer and a second layer arealternately laminated, which is characterized in that a polyester (A)constituting the first layer ispolyethylene-2,6-naphthalenedicarboxylate; a polyester (B) constitutingthe second layer is a polyester containing at least one of an ethyleneterephthalate component and an ethylene naphthalene dicarboxylatecomponent; an average reflectance within a wavelength range of 400 to750 nm is not more than 25%; an average reflectance within a wavelengthrange of 800 to 1,200 nm is 50% or more; and a Young's modulus of thefilm at 90° C. is 2,400 MPa or more in at least one direction of thelongitudinal direction and the lateral direction of the film.
 2. Thebiaxially stretched laminated polyester film according to claim 1,having a protective layer composed of a polymer having a glasstransition temperature of 90° C. or higher and having a thickness of 5μm or more and not more than 20 μm on the both sides of a laminatedstructure portion (I) in which the first layer and the second layer arealternately laminated.
 3. The biaxially stretched laminated polyesterfilm according to claim 2, wherein the polyester (B) constituting thesecond layer is a polyester containing 50% by mole or more and not morethan 95% by mole of an ethylene terephthalate component on the basis ofthe whole recurring units.
 4. The biaxially stretched laminatedpolyester film according to claim 2, wherein the polyester (B)constituting the second layer is copolymerized polyethyleneterephthalate having a glass transition temperature of lower than 90° C.5. The biaxially stretched laminated polyester film according to claim1, wherein the biaxially stretched laminated polyester film is composedof only a laminated structure portion (I) in which the first layer andthe second layer are alternately laminated; or is a film in which aprotective layer having a thickness of less than 5 μm is provided on theboth sides thereof, the polyester (B) constituting the second layer iscomposed of a polyester having a glass transition temperature of lowerthan 90° C., and a Young's modulus of the film at 20° C. is 5,000 MPa ormore in at least one direction of the longitudinal direction and thelateral direction of the film.
 6. The biaxially stretched laminatedpolyester film according to claim 1, wherein the polyester (B)constituting the second layer is a polyester having a glass transitiontemperature of 90° C. or higher.
 7. The biaxially stretched laminatedpolyester film according to claim 6, wherein the polyester (B)constituting the second layer is a polyester containing 30% by mole ormore and not more than 90% by mole of an ethylene naphthalenedicarboxylate component on the basis of the whole recurring units. 8.The biaxially stretched laminated polyester film according to claim 1,wherein the polyester (A) constituting the first layer ispolyethylene-2,6-naphthalenedicarboxylate having a copolymerizationamount of not more than 8% by mole on the basis of the whole recurringunits.
 9. The biaxially stretched laminated polyester film according toclaim 1, having at least one layer containing an ultraviolet lightabsorber.
 10. The biaxially stretched laminated polyester film accordingto claim 9, wherein the ultraviolet light absorber has an extinctioncoefficient E at a wavelength of 380 nm of 2 or more.
 11. The biaxiallystretched laminated polyester film according to claim 9, wherein anaverage light transmittance within a wavelength range of 300 nm or moreand less than 400 nm is not more than 10%.
 12. The biaxially stretchedlaminated polyester film according to claim 1, which is used forshielding of heat rays.
 13. The biaxially stretched laminated polyesterfilm according to claim 1, which is used for laminated glass.
 14. Thebiaxially stretched laminated polyester film according to claim 1,wherein a coating layer having a refractive index of 1.60 to 1.63 and athickness of 0.05 to 0.2 μm is provided on at least one surface of thebiaxially stretched laminated polyester film having the laminatedstructure portion (I).
 15. An infrared light shielding structure forlaminated glass comprising the biaxially stretched laminated polyesterfilm according to claim 1 having a laminate of a metal and/or a metaloxide laminated on one surface thereof, wherein in the biaxiallystretched laminated polyester film, a thickness of the protective layeron the side coming into contact with the laminate of a metal and/or ametal oxide is 5 μm or more and not more than 20 μm; the laminate of ametal and/or a metal oxide has a laminated structure (II) in which alow-refractive index layer and a high-refractive index layer arealternately laminated; and the infrared light shielding structure forlaminated glass has an average reflectance in a wavelength range of 400to 750 nm of not more than 30%, an average reflectance in a wavelengthrange of 800 to 1,200 nm of 50% or more, and an average reflectance in awavelength range of 1,200 to 2,100 nm of 50% or more.
 16. A laminatedglass comprising two glass sheets having the biaxially stretchedlaminated polyester film according to claim 1 sandwiched therebetweenvia a resin layer composed of at least one member selected from anethylene-vinyl acetate copolymer, polyvinyl butyral, and an ionomerresin.
 17. A laminated glass comprising two glass sheets having theinfrared light shielding structure for laminated glass according toclaim 15 sandwiched therebetween via a resin layer composed of at leastone member selected from an ethylene-vinyl acetate copolymer, polyvinylbutyral, and an ionomer resin.
 18. The biaxially stretched laminatedpolyester film according to claim 3, wherein the polyester (B)constituting the second layer is copolymerized polyethyleneterephthalate having a glass transition temperature of lower than 90° C.19. The biaxially stretched laminated polyester film according to claim2, wherein the polyester (B) constituting the second layer is apolyester having a glass transition temperature of 90° C. or higher. 20.The biaxially stretched laminated polyester film according to claim 10,wherein an average light transmittance within a wavelength range of 300nm or more and less than 400 nm is not more than 10%.